- Jul 1, 2020
As it is, I would be very curious to A/B the M12 and the C658 to see if there is any audible difference.
As it so happens, I have the M12, C388, Node2i, and between the time I started reading this thread and getting to this page 13/14 of the thread, ordered and received the C658, swapped the HDM-2 MDC card from the M12 into the C658 - and sat for a quick listen (last night). I'm also familiar with miniDSP (a discussion in this thread), and have/used; DDRC-88A/BM, 4x10HD, nanoDIGI 2x8, and 2x4HD - these have been used as crossovers for LXmini speakers and a stereo pair of open-baffle Phoenix (alternate) subs - all Linkwitz designed DIY speakers.
First impressions of the SQ difference between M12 and C658 (without Dirac so far) - M12 wins on natural 'fluid' presentation and stereo separation - I suspect that's due to the AKM DACs, think M12 has separate DAC for each channel (with each 2ch DAC being used in mono to smooth results), lower noise rating, vastly-configurable stereo sub and line outs, and overall better build and other components including case and isolation. Also goes without saying, M12 has a larger, touch-enabled screen, and the menu system is thorough (many more configuration possibilities), and is a genuin pleasure to use.
The C658 has a newer firmware update system (all happens through BluOS update), which is much easier than the old USB-stick system of M12 and C388 generations. Another benefit of C658 is the 5GHz wifi (better connection). Then there is Dirac, which the M12 doesn't have - despite my requesting a Dirac MDC card from NAD on several occasions (as if they care what I want). I find the C658 menu system ready to use, very limited (compared to M12) and overall extremely under-utilized by NAD dev team (pales in comparison even to the previous generation C388 - which does make use of the screen color capability).
In the used market, C658 is selling around $1k, and M12 around $2.5k. Depending on what a person is looking for, both are great units, and both could be so much better with more development time accomplished through firmware updates. So much potential with these products if NAD would allocate more resources to it (especially with the M12). I suspect the C658 is already performing very near its hardware limits (SQ-wise) and suspect the M12 firmware is leaving a lot on the table (which is sad).