Thanks!
For the AC, there is a little splitter in there like this one:
Amazon product ASIN B01GSFFEOC
The Radial is purely to mix an external source like Aviom or Allen-Heath ME-1's. The ME-1/Avioms have headphone outputs that I bring into the Radial to match impedances and convert to XLR Balanced Inputs (Input 3).
In all my presets, I take those XLR Balanced Inputs (Input 3) and mix my Guitar Signal directly into it. That feed then goes direct to my PSM300 for IEMs (Output 2). The main XLR Outputs (1) feed FOH.
We always have a silent stage, everyone has IEMs with full-band mixes however they want. For regular band gigs, I don't use the Radial. I sit that rack right on-top of my other SKB Rack w/Allen-Heath Qu-Pac mixer and pull the XLR's that go to the Radial directly to the mixer. Everyone has their own app on the their phone to control their personal mix however they want.
Seems to be super snug! I believe they are simple self tapping screws that I used.