It certainly looks like a more than capable board, so with no way of knowing if everything is functioning as it should, I suppose it’s down/back to a process of elimination.
It sounds like you’ve had a fair bit of trouble with several DACs and it honestly does not seem the issue atm.
Without specific details only you could have as to what went wrong (and when) with the other DACs, it’s hard to know if some aspect of the onboard HD audio hardware has been involved in the past.
That’s of course assuming the same motherboard w. the other DACs and that you don’t already know the reason for the other failures or audio degradation with them.
With 5 HD audio outputs and a Headphone amp stated to be capable of driving 300ohm headphones, along with myriad settings, options etc., there’s obviously a process of eliminating to do (like you don’t already know that
I suppose if it were me, I’d disable every audio output except the HD digital out you use to the DACMagic+ and see when/where and if the USB audio problem persists under various configurations.
It really doesn’t sound like it’s the DAC Magic + at all to me.
Also, you seem to know plenty about your gear and I don’t/can’t know enough about your set-up (which has a lot of audio related gaming options) to make a proper diagnosis as to what might be affecting the USB audio-out, to allow for an offer of any specific suggestions.
If you engage the onboard HD audio (analog) headphone amp simultaneously, while using the USB HD digital out, there should be an option to disable it and all other audio device out out in the device manager.
I use Windows 7 Pro 64 bit and have an older Intel LGA1555 socket based board.
So for audio, just HD audio-out is in use and I rarely even enable the analog mimi-RCAs on front or back.
There’s been a couple of times I needed to update the audio chipset firmware/driver over the years.
As an aside, even when things work as they should on any Win 7 PC, it won’t output 24/88.2 or 24/176 without some kind of signal “handling” internally or before being sent to a DAC. I believe that’s fixed in Win 10.
But no matter the OS, I don’t envy the job you have sorting this out.
I suppose what I’m trying to say (likely with too many words) is that there are simply so many possibilities for degraded audio, that it sometimes depends on what your time is worth and whether you have access to another PC outputting a signal under the same parameter, to be able to determine if it’s worth sorting the source of things on the PC end.
Maybe you could pop in a “borrowed” PCIe sound card and see what you get. If it’s inappropriate and doesn’t do what you want it to, you can return it (or If it fixes things, maybe keep using it)?
I hate that all I can say after all these words is “good luck”. But I do hope you get things sorted and that any suggestions haven’t proved to make things even more frustrating!
(Maybe you solved things in the time it took to track down your mainboard and write all this! )