Hi. The subwoofer output allows you the option of sending bass frequencies to an external powered sub, but it doesn't require it. You can download the owner's manual from Onkyo to look at the specifics [STRIKE], but that receiver will allow you to set up the bass management the way that you want - either having the full range sent to your main speakers, to have full range sent to your main speakers and bass sent to the sub, or to use a crossover and send bass to the sub and the rest to the main speakers[/STRIKE].
EDIT: OOPS! I think that I was wrong about that. I'm still looking for details in the manual, but I don't see any bass management. I'll update in a few minutes.
EDIT 2: Yeah, after combing the manual and searching the web, I'm pretty confident that receiver doesn't do any bass management. However, I do still think that the subwoofer pre-out is an option and not a requirement. I'll keep looking.
EDIT 3: Alright, I've used up my web mojo. I can't find the answer. Sorry about that.