I have all the wiring diagrams for a '21 Bose CX-5, including pin outs. I added a sub and first made my own t-harness to pig tail off the sub wires in trunk, signal definitely filtered/processed by Bose amp (duh). I then took a gamble and ordered a General Motors Bose harness. 2/3 connectors fit. One 16 pin black, one 16 pin green, and one 8 pin black. Unfortunately the one that doesn't fit is the black 8 pin which carries the sub signal from TAU -> Bose amp. I took another gamble and soldered everything up on the green 16 pin which carries the front and rear speaker signals, and then ran a length of speaker wire (taking care to use the correct pins for + and -, from the Bose input side) to the trunk in the hope that the door speaker signals would be flat pre-bose, which to my ears, is not the case. This leads me to believe one of two things, either A) everything coming out of the head unit or TAU is already processed and rolled off, or B) the door speakers are rolled off from the head unit. I think option A is more likely, but have yet to test the signals coming out of the head unit to confirm this theory. I could t-tap into the sub signal wires pre-bose, but I am trying to avoid cutting any factory wiring at this point since I'm still unsure whether Mazda has the head unit sending out a processed signal.