I tired various combos. First used the factory sub wires as inputs, GN / BK (-), BU / GY (+).
It was too narrow of a frequency band for a better performing sub and sounded muted.
Then I tried just the yellow/yellow black from the right hand front doors. It was better. I then tried a combo of the factory sub and the front right door speakers thinking a broader frequency spectrum to send to the processor in the amp. A little better. I then went to front left door and front right door, BN/BU (-) BU (+), YE / BK (-) YE (+). That was the best. My kicker amp with keylock takes two speaker channels for inputs then does its processing.
Your results may differ based on amp and DSP used but using both front channels was the best by far.
I just tapped in to the wires coming out of the factory Bose amp which made checking easy. I had to cut all the wires anyways to run them in to my amps then ran all new speaker wires from amps to speakers. I used 4 wire sheathed bundles going to each door and have the tweeters and woofers on their own channels off my 8 channel amp so that solved those other OEM issues.
I found OEM sub signal is very narrow and very weak. Also drops off as volume is raised. The rear door speakers have virtually no signal. Don’t tap those.