What do you mean on long term stability ?
It’s worth it to spend some time reading all the technical posts that James and the dCS team have shared.
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I’m very interested in these threads b/c many claim improved clocking is essential to unlocking the natural, or analog, presentation of digital.
I think a Rossini or Vivaldi DAC, paired with a Vivaldi clock And an external ultra-precise clock is a fascinating combination, and envy those who currently enjoy it. I also find it interesting that dCS contemplated this combination for “super” users.
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I think a key factor that needs to be considered here is cost. Manufacturers of DACs have a lot of different components they need to consider when trying to hit a certain price point. When allocating costs they could well conclude that money for a more expensive clock makes a bigger difference to sound when spent elsewhere.
After market clock vendors on the other hand will focus only on the clock and will be able to allocate more cost to the clock itself. That being said, the peformance criteria they focus on may not be the ones that a particular device needs, so there’s still no clear right answer.
James’ explanation of why the Vivaldi clock doesn’t care so much about short term stability makes sense. But logically speaking I also can’t underand how long term stability is relevant to sound quality. Long term stabiliy is talking about consitent performance over years. An audio track is measured in minutes, and jitter in even smaller intervals than that. Any of these clocks will be incredibly stable over these short periods of time.
I would agree that it is possible third party or aftermarket vendors could allocate resources in such a way as to refine or improve an offering. Seems to me certain power supplies are a good example. But where the device is already in the wheelhouse of the OEM company, I think the odds of that aftermarket company being better at it than the OEM go down. I am not saying it is impossible; I just see it as unlikely absent some specific evidence that they have the resources or expertise. I could start assembling reference clocks at my home and devote 100% of my time and money toward that effort, and I still couldn’t match in 100 years what dCS do in a month. Without competitive resources, the focus is not enough.
I found James’ explanations here instructive. I don’t think the argument is that long term stability itself directly contributes to SQ (which is part of Paul McGowan’s red herring claim that rubidium clocks are a “myth”). I read this as implicitly stating that the addition of the long term accuracy helps to make the Vivaldi Master Clock better at what it does. But I’m no engineer, so I have to accept it as stated, or look for more dis/proof.
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I agree that dcs may have thought that the likely development of an atomic clock to clock their clock may be beyond their immediate scope and not specifically salable because the highly accurate clock that is designed for a scientific purpose already exists. For dcs to add lets say another $5,000 - $15000 component that already exists and then putting it into a beautiful shell another few grand may not be a big seller. Sure they would sell some but only the most anal or highest rollers would pay lets say $10-15000 so the clock to clock the clock would match. A lot of tooling and effort for a low volume seller. I think their boxing everything into a box like vivaldi one shows that they recognize the market is toward the lower price but the flagship is quite pricy already. Kind of like dan d’agostino developing the relentless … not for your average high end buyer.
The way that i rationalize the use of an atomic clock thinks more in terms overall accuracy. My thought being more conceptual without extensive research or formal training. The vivaldi clock is excellent at clocking something in a short interval, possibly cycles of amplitude and frequency where jitter is predominant but over a prolonged time more than a number of cycles doesn’t maintain its accuracy ill call drift. My thought is that most listeners arent sensitive to these shifts in time to the extent that the jitter is minimized. Im guessin measured in errors over a period of time. Now we’re talking really fast and minute oscillations. The atomic clock isnt extremely accurate in clocking these shorter oscillations and controlling jitter having more variation in amplitude and frequency in the micro view but over a longer number of oscillations is extremely accurate - having variations in in the individual cycle where jitter occurs but much more accurate at reaching some long term finish line. This big picture clock doesn’t override the short timer accuracy controlling jitter but improves its tendency to maintain its overall accuracy and our ear/brain notices the change in accuracy and thereby SQ. Not a technical explanation but how i rationalize to myself the purchase one. 
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I stumbled into this thread wondering who else was using Stanford Research Systems rubidium clocks in their audio systems.
I use the SRS FS725 frequency standard - this is the “lab” unit rather than the “audiophile” PERF10. It has a more compact form factor and fewer LEDs! Note that the output is 50 ohm impedance, NOT the usual 75 ohm for digital audio so take care with the cable.
My DAC is the Esoteric K-01XS, and the sonic changes are slight but noticeable - extreme treble is improved and spatial cues are better defined.
The guts of the FS725 is the same SRS PRS10 used in Esoteric’s $20k+ device.
As a fun project I built a time of day clock, using small scale integrated circuits as an exercise, driven by the 1pps TTL level output. In a few thousand years it will need to be reset!
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I have the perf
As I understand it the 50 ohm-outputting FS725 wouldn’t work properly with dCS gear, which wants a 75 ohm input. The Perf10 outputs the desired 75 ohms, though.
Just checked the input specs of your rather delicious K-01XS — 50 ohms 
I’ve said it before…I wish my Perf10 looked nicer than it does. It makes me giggle that SRS said that the lights were an “audiophile” addition. Bloody horrible-looking thing. Subtle but welcome audio quality improvements, though.
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I dont think its as subtle but i do like the extra light when exiting the room at night after the lighting goes down
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Have you considered these: https://www.lightdims.com/index.php
I use them in many spots in my bat cave of an A/V room. Work very well and come in a myriad of sizes.
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That’s pretty cool. Thanks Steve.
That is cool, Steve. Bookmarked for future dressing of less objectionable components!
The Perf10 needs a sticker…oooh…around about 19" × 3.5" in size to look bearable to me. Having it anywhere near the rest of the kit just turns my stomach. It lives under the rack, doing its Nightrider thang in private.
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Thank you! That’s why I come to this forum, for these little tidbits of information. I agree the unit looks hideous, but there is an appreciable improvement of the presentation to keep it in my system.
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Interesting
On an unrelated note regarding the Vivaldi clock, does anybody know if it is normal for the clock to shut down about 15 seconds after I power it on every time?
That sounds like “no.”
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I have it plugged into my power conditioner and when i turn the power on, it comes on, but then shuts down 15 seconds later. Then, if i turn it on, it stays on…. No such things happening with my streamer or dac
That is not normal. I have mine plugged into my Shunyata power conditioner and it has been on for a few years and never turned off. Is it possible that there is some sort of cabling issue? I assume your clock cables are all 75ohm. If you go through the same procedure without any clock cabling do these same symptoms arise? Have you contacted your dealer about this? Very odd.