Like yourself I was also just going to go ND555, as like you I have a 552dr and at the time a naim NDS, running 2 power supplies. After picking up a nd555 and swapping it over with the nds, I couldn’t tell a difference at all, nor could my daughter or anyone, so I took it and my nds to the dealer as I thought it could just be my system. Well at the dealer and on a full naim 500 system the same, I couldn’t tell any difference, the dealers helper said the same, the dealer tried to say it had better bass, more air, etc, etc, but no it didn’t.
So that was for me the nd555 out and so went looking for something else, at this point I had never heard of dCS and the Bartok was my introduction and very nice it was too, different sound to the nds, I would say the nds was more like an analog sound and the Bartok certainly sounded more alive and full of detail, without being cold, but certainly not warm, if you get what I am trying to say.
All was fine and I could have certainly gone with the Bartok over my nds, plus the extra benefits the dCS has over it was very appealing, especially going forward and the upgrades that dCS tend to offer free.
But me having mentioned my thoughts on the Bartok, said dealer said, let me go get the rossini and clock, well this was just something else, it made the hairs stand up on my arms, I was simply blown away with how good it was going through the naim 500 system, only problem was price, but I knew this was what I wanted.
It has everything the naim had, but on top of that just more lovely details, it just made you want to play more and more and had you on the edge of your seat waiting to hear things that you had never heard before on your favourite tracks, I could have sat in that chair all day and that has only ever happened to me twice, this time and many years ago when I was in a London hifi shop down Tottenham Court Road and I first heard the top naim system, 52, active 135s etc into dbls I think, anyway I couldn’t stop thinking about the rossini.
Obviously I ended up with one and the clock, the clock does make a nice difference, not one you hear straight away, but after a few days or a week, forget to switch it on like I have twice and you will probably find yourself sitting there thinking, this doesn’t sound right.
So my advice is get a rossini and clock if you can, secondhand like mine is a great way and right now a pair is for sale at £15k, still a lot but not much more than a new Bartok.
Also I found the jump in performance from the Bartok to rossini to be a much better step up than the rossini to vivaldi was, yes the vivaldi is better but for the added outlay I am not so sure, but then only you can decide that.
Finally I now run my dCS into my 552dr and 500dr then to pmc fact 12 speaker’s and I also use witchhat morgana cables everywhere I can, even the 552 burndy and they suit it all lovely
Hopefully this has helped