First, I don't use a Bel Canto DAC, I use a Benchmark USB version. However I do use it with a ZP-90.
The sound quality of the ZP-90 with almost any external DAC will be better than the analog outputs of the ZP-90.
If possible use the ZP-90 with "fixed" output for the best performance. Otherwise, try to keep the Sonos software volume control under about 75%.
Possibly the most important consideration is "jitter". The external DAC needs to have good jitter reduction, or a jitter reduction device, or a mod done to the ZP-90 to reduce jitter. It's important and can easily add another $500 to the cost.
Paul
The sound quality of the ZP-90 with almost any external DAC will be better than the analog outputs of the ZP-90.
If possible use the ZP-90 with "fixed" output for the best performance. Otherwise, try to keep the Sonos software volume control under about 75%.
Possibly the most important consideration is "jitter". The external DAC needs to have good jitter reduction, or a jitter reduction device, or a mod done to the ZP-90 to reduce jitter. It's important and can easily add another $500 to the cost.
Paul