Sonos is plenty good for the High End, or else I would not use it in my listening room.
You may wish to have it modded and I'm sure there is substantial improvement to it - something I may pursue in time. However, you can get very good results simply by taking the dig. coaxial signal out of it into the outboard DAC, as you have done.
The quality of the DAC is of monumental importance. You are wise to seek a 32 bit DAC, however there is a large variation on how these DACs sound, so it would be advantageous to hear two or three in your room if so inclined.
The digital cable is critical; there are different levels of sound quality between digital cables, and one has to try two or three to find an optimum result.
Some RCA interconnects perform better as digital cables than other competitors' digital cables! So, if you have alternatives lying around, try them. Typically, use of an RCA interconnect will warm up/plump the low end and attenuate the treble, causing the system to sound more mellow, but there will be some loss of treble detail and some loss of extension/depth of the soundstage. Ideally you will find a coax digital cable which will give you all the performance you want in every respect, but this is a good compromise solution to tame a hot high end.
You need to make a decision on whether to continue to run a DAC with a pre/vol. control or not. The DACs I have used with vol. control have been compromised in terms of absolute sound quality. I prefer use of a dedicated DAC with set output and a separate preamp. You might find a DAC with a vol. control which is not significantly influenced by the compromise of having both functions together, but it might cost you about $5K to find one which doesn't compromise.
I have compared Sonos/DAC combos to iTunes and JRiver via USB file playback and it holds its own. With the advent of the 32 bit processing DACs the issue of missing out on Hi Rez files is reduced imo. I don't care for much of the music currently on Hi Rez downloads, but I'm getting better sound quality from CD playback via a 32 bit DAC than what imo 24 bit players can provide. So, there's not much to complain about. :)
You may wish to have it modded and I'm sure there is substantial improvement to it - something I may pursue in time. However, you can get very good results simply by taking the dig. coaxial signal out of it into the outboard DAC, as you have done.
The quality of the DAC is of monumental importance. You are wise to seek a 32 bit DAC, however there is a large variation on how these DACs sound, so it would be advantageous to hear two or three in your room if so inclined.
The digital cable is critical; there are different levels of sound quality between digital cables, and one has to try two or three to find an optimum result.
Some RCA interconnects perform better as digital cables than other competitors' digital cables! So, if you have alternatives lying around, try them. Typically, use of an RCA interconnect will warm up/plump the low end and attenuate the treble, causing the system to sound more mellow, but there will be some loss of treble detail and some loss of extension/depth of the soundstage. Ideally you will find a coax digital cable which will give you all the performance you want in every respect, but this is a good compromise solution to tame a hot high end.
You need to make a decision on whether to continue to run a DAC with a pre/vol. control or not. The DACs I have used with vol. control have been compromised in terms of absolute sound quality. I prefer use of a dedicated DAC with set output and a separate preamp. You might find a DAC with a vol. control which is not significantly influenced by the compromise of having both functions together, but it might cost you about $5K to find one which doesn't compromise.
I have compared Sonos/DAC combos to iTunes and JRiver via USB file playback and it holds its own. With the advent of the 32 bit processing DACs the issue of missing out on Hi Rez files is reduced imo. I don't care for much of the music currently on Hi Rez downloads, but I'm getting better sound quality from CD playback via a 32 bit DAC than what imo 24 bit players can provide. So, there's not much to complain about. :)