d3vi0uz
Welcome to the AH forum and I hope you have some great trips here for information. There's a ton of expertise here and lots of help.
First things first, I gotta get this off my brain: you have schiit in your setup.
I apologize.
Ok, now that we're passed that, I would probably start off with questions rather than answers.
You have a really nice, current, set of powered speakers. Good looking stuff. I'm unfamiliar with Mackie,but having done a little reading, you have made some good choices with those. Powered speakers may very well be the future in many areas of audio.
Where my questions start is the marriage of the Schiit equipment and the Mackie. The Schiits don't appear to have a line level output, just an RCA L and R output. Your Mackie appears to like 1/4" XLR balanced/unbalanced inputs or a single stereo line level input. So my first question is did you choose that marriage on purpose? How are you making those two make sweet music?
The subwoofer question sounds like an offshoot of my first question. Most subs have a rear volume control that is set at setup and calibration time. You match it with the levels of the L and R. Then, as you drive up the volume to the trio, they all increase and decrease together. If you don't have the right signal (line level or a proper XLR connection) then you may be goofed up on your sub and that's why it isn't working like you think.
I haven't see a setup like this one. I'd be interested in your thought process for putting it together like you have. There are many powered speaker officianados here so if you can explain it, I'm sure the braintrust can help out.
Again, welcome and I hope you get some good help.