Best PC motherboards for USB Audio?

The best sounding motherboard is no motherboard. PC audio is a challenge, and unless you want to consider a lot of pricey stuff to compensate, you are better off investing in a dedicated streamer/network player.
Not to retype same stuff for 100th time, but in essence you want to eliminate processes running, minimize OS(think Linux)go to small linear power supply and separate your power and signal where you can. Keeping mechanical drives in another room and connect ideally by ethernet will also be a big improvement. computeraudiophile site is expert on much of the related minutia I mention, although plenty of related comments here. Cheers,
Spencer

The soundcard’s amount of jitter is actually pretty irrelevant, as any decent DAC (even cheap DACs will reduce jitter to below CD quality and better ones to below 24Bit quality. As long as it’s not a random one you found on eBay, you’ll be fine.

You know, it’s not IMHO the PC or the motherboard, but the PC’s power supply noise. Try to keep the PC’s power supply outside of your surge protection / AC noise filtering devices. Or at least put the on separate. Also if possible, experiment via the PC’s optical out as well. Kind of tricky part: Keep PC and audio on same AC circuit if using electrical based contacts.

In theory, USB is best due to the DAC’s ability to pull based on it’s internal clock, but sometimes the galvanic (electrical) isolation of the optical cable is superior.

I use a Raspberry Pi based streamer which uses a little bitty wall wart, and I keep that on a different surge protection. I should consider getting a linear supply for it instead.

As I was thinking about my streamer, I found that iFi makes a nice range of replacement wall warts you can use for your network components (router, switches, Raspberry Pi) :
https://amzn.to/2KLCzre
Fairly reasonably priced as far as Audiophile accessories go.