@asw The NAD C-658 is probably the BluOS streamer/pre-amp/DAC you're referring to. It is part of the "Classic" (C-***) series. It uses ESS-Sabre 32bit DAC and includes MM phono stage, DiracLive bass correction (and pay-upgrade to full-freq. version) and balanced outs. It earned top-honors by What-HiFi, Sound & Vision, etc. I don't have experience with this unit, but it is a compelling option.
I do have the C-388 digital integrated amp (with HDMI-2 and BluOS2i MDC modules), and am extremely fond of this all-in-one unit in my 2-ch system. I chose C-388 over the M32 because C-388 has Speaker A/B capability (M32 does not). I use this unit as a source to feed miniDSP4x10HD that functions as a crossover to drive LXmini speakers via 12-ch ATI (class AB) amp. Sometimes, I also listen to a set of Martin Logan electrostats directly from the C-388, normally I route ML's through the miniDSP also - since there are pleanty of amp channels, and it allows taming ML bass and extending the highs (by DSP) - makes them sound better to me. NAD C-388 uses the Burr-Brown PCM-1794(a?).
I recently tried something on the advice of Danny at GR Research (who said the poor-quality DACs in NAD and miniDSP were likely veiling the sound). I purchased two highly-rated (SINAD) Topping E30 DACs, and ran the digital signal (from optical source) direct to miniDSP nanoDIGI (which has 2 digital coax in, DSP processing, and 4 digital coax out) to the Topping DACs for full digital signal till DACs RCA-out to ATI amp. After a couple weeks of listening and playing with DAC filters, my conclusion was...
- It can be made to work -
actually works great!
- It sounded different - and adjustable with DAC filters
- It doesn't sound better - to me in my room
Returned the Topping DACs (cost $5), and went back to built-in miniDSP4x10HD DACs. It was a worthwhile exercise and fun experiment - just didn't improve SQ.