ok, the way this hu works, with only one preout is like so, as long as there is not dedicated sub output:

the RCA output is really for a rear speaker amp.

this means that when you are playing a cd or listening to the radio, if you fade more to the rear speakers not only will more sound come from the rear speakers, the subs will also be louder

this also means that if the bass is set low on the hu for the rear speakers, it will also be low for the sub. now if this hu dosen't have an independent bass and treble setting, and only its rock, jazz, classical crap seriously get rid of it and get a nice alpine hu

pyle=crapo