can i do this on my pioneer p4000 deck?

i would rather have my speakers play the mids/highs so they dont distort as i turn it up

stock subwoofer? The stock amplifier as far as i no can't be adjusted per channel. Pretty much changing the highs/lows/mids on the rear speakers also affect the sub. I know there are bass cancellors that u can put in line with the speaker wires. So if u get the right one of those, u should be able to increase bass and have it only affect the sub.

ya you need an aftermarket amp to do so. but yes there is sub control on that deck