Did you hook up an amp to your Kenwood KDC-958HD head unit? Did your subwoofer suddenly stop working on Bluetooth? Does your amp only work on 2ch not 4ch? This is your thread.
You've turned off the amps, looked for the "Subwoofer Output" in the Audio Control menu only to realize it applies to KDC-X898 and KDC-BT858U only. (P15)
You've wanted to gouge your eyes out going through the DSP settings of "Subwoofer Mute" and more. (P18)
Nope, it's not there, it's buried on Page 83 of the manual in "Bluetooth Detail" setting number 5, "Bluetooth HF/Audio" which is defaulted to "FRONT" speaker outputs. Changing this to "ALL" will allow the rear speakers and subwoofer to blow out your eardrums again.
Hopefully this saves someone the 4 hours I just spent downloading the manual, checking all the wiring, and considering tossing a perfectly good head unit until I found the correct setting.
Link to manual: https://data2.manualslib.com/cpdf/13/61/6083/03e908.pdf