If you want to buy an AIO I bet it's not going to be as good as stand alone units.
Do you really need something to mix the sound and voice together , also a mic input?
What headphones do you have? Sensitivity w/ the impedance of a headphone will tell you how much power is required to hit X SPL
I'm willing to bet that this mixamp is garbage, however this is my opinion.
https://www.astrogaming.ca/mixamps/MIXAMP-TR.html?dwvar_MIXAMP-TR_color=Black#start=1
Yeah, no.
OP- Try looking at True-Fi depending on your headphones you have. They have a free trial aswell. The only downside is you can't change the preset other than how much bass is boosted.
Personally I would look at powered bookshelves or passive from companies like JBL, SVS, Emotiva etc.
Since you’re going to have to send power to each one anyways, I would say search for passive with a receiver or Dac/amp as separate.