The 0.2V and 0.6V output settings were added as a reaction to modern streaming technologies – AirPlay connecting to your system, whacking the volume up to full and blowing some drivers for example is not fun. Lower output voltages are a useful safeguard against such things. I once serviced a speaker which spat a voice coil across the room because of a smartphone jumping from being connected to the user’s car to their streamer via Bluetooth – by all accounts it gave the cat a hell of a jump.
With that said, to my knowledge in the event of night-time listening where a lower volume is required, the benefit of using a lower output voltage setting and keeping the volume control towards the top end of the range is that with a lower output voltage and higher volume control for quiet listening you keep the signal to noise ratio in the Ring DAC itself higher, as the volume control stage immediately precedes the FPGA’s output to the Ring DAC whereas the output voltage setting takes place after the D/A conversion. The signal to noise in the analogue output stage will still be lower whether using a lower output voltage or a higher voltage but lower volume control, but the conversion stage retains a higher ratio with a lower output voltage in this case. My advice would be to use whatever output voltage setting that allows for higher range usage of the volume control – though I will double check this point on Monday.
Talking about the volume control implementation used in dCS DACs, given the fact that the volume control is simply the last step in what could easily be a very long stage of digital filtering, if working at a lower volume control meant the maths behind this processing was in some way flawed and could create a loss of dynamics in itself, the effects of digital filtering would be pretty horrendous. This definitely isn’t the case when done correctly. The argument is therefore not whether a digital volume control is the correct way vs analogue, to my mind the conversation is actually around whether volume control pre-D/A conversion or post using one of a variety of methods is most appropriate. That becomes incredibly tricky to draw anything meaningful from, because the art of product design is being aware of the trade-offs with different approaches and striking a good balance between the competing compromises. It is possible to get good results with either, and I have no doubt every approach has been considered over the decades with a dCS product. From conversations with our engineers on these topics, honestly the sheer number of angles that are considered when designing each stage of a dCS DAC are genuinely staggering.
I will say that as is the case with every area of dCS products I have ever thoroughly investigated, the system as a whole and end user experience as a whole has been taken into consideration. We aren’t in the game to make products which will win at spec sheet comparisons, we are out to make ones that are at the forefront of what is possible for sound quality. For example, if digital purity was the name of the game, even at the expense of the “end product”, one could simply connect the DAC outputs to the output jacks of the product and let whatever is on the other end of it deal with load matching and such. Adding a line output stage to the DAC will add in the “downsides” an analogue stage will naturally bring (distortion, noise etc.), but will likely allow cables and (unknown) input stages down the chain to be driven much better than would be possible simply by connecting the DAC output directly. This is what, from a spec sheet, would be seen as a compromise in the unit design – but it is one that in the real world results in an improvement in system performance.
I appreciate this may not be a popular opinion in some areas of the internet, but any opportunity for blind testing should be taken where possible when A/B comparing kit. If sound quality is king to you, let your ears be the judge, not the parts of all our brains that are predisposed to want us to think a certain way about a piece of equipment. If that test concludes you prefer the preamp in the system, more power to you (I‘m sure there is a bad pun in there somewhere)!