Great job on your stereo integration. I have a nib a massive BX4 that I'm going to use for my Vw build. I also had a BX2 that I was going to bridge to power my Kenwood Excelon flat subwoofer, but I sold them both to another Legacy owner.
My Subaru is set as follows,
Alpine IVE W530 as my source
Pioneer stage4 6.5 components with the tweeters of axis in my A pillars
Powering those is my Mosconi AS100.4 amp
No rear fill
CDT QES1220 SQ subwoofer
Powering that is my Mosconi Zero3 amp bridged
As far as processing since I run active is my Zapco DSP Z8...