Yeah its through the sub pre-outs. On my radio its in the same menu as treble/bass controls and it says "sub". You can turn the sub(s) off, or range themanywhere from -10dbs to +10dbs. I find it useful because I can change the level according to the song thats playing.

 

aka sub control

I still think the switch would be better since you dont have to go through all the menus n such