Lag free side tone plus amp/DAC for headphones

I picked up the sound blaster g6 for my x2hr. Their claim to having side tone, while technically true, is unusable due to the lag. Also, it’s too finicky and I’ve found I don’t like software and don’t want a gaming specific amp/dac solution. I already have that in the form of my Astro mixamp which works perfectly and drives the x2hr no problem. However, as I mentioned in my other post, I’m giving away my old Astros to my son as soon as I’m squared away with this upgrade.

So now I have my eyes on a used schiit stack as I figure that would give me a good foundation for any future upgrades even though it might be a little overkill for the x2hr at the moment. Basically, I just want whatever the sound signature is from the headphones+amp+dac with no proprietary software to fiddle with.

Here’s the questions:

How does one connect an audio interface like the Behringer MA400 to something like the schiit stack? Obviously the ma400 would provide lag free mic monitoring which is what I’m searching for. But how do I also get the feed from the audio source (PC games) into the headphones? How does all this stuff connect?

If you don’t need anything specific from the DAC/AMP itself the Behringer UMC22.

The dac part: I can’t tell any hiss or distortion at any volume on my Sundara’s or KPH30i’s.
The amp part: Not very powerful, wouldn’t drive any planars off of it but any lower impedence (-100ohm?) will be fine.
The side tone: lag free to my ear and no software needed, just a knob to turn higher or lower.