What is the opinion of Reddit about the
TASCAM US-366 4-In/6-Out or 6-In/4-Out USB Audio Interface?

Get one of these: http://www.amazon.com/TASCAM-US-366-6-Out-4-Out-Interface/dp/B00B7DN59W/ref=sr_1_1?ie=UTF8&qid=1445234991&sr=8-1&keywords=tascam+us+366

You can run your Xbox into it via Optical.
You’re PC can plug in via the RCA in/out.
It has a monitor (speaker) out as well as a headphone out.

I had one, they’re pretty good.

I found this fella too. Optical, coax, XLR and usb in, balanced TRS out.

https://www.amazon.com/TASCAM-US-366-6-Out-4-Out-Interface/dp/B00B7DN59W/ref=mp_s_a_1_2?keywords=optical+in+balanced+interface&qid=1559990750&s=gateway&sr=8-2

This is the cheapest mixer I could fine with optical.

At that price you’re better off spending a little more and getting a full HT receiver from accessories4less.