I'm going to assume from your post that you do not have a subwoofer?
I have the 5760 and what you would need to do to feed all of the bass to the front mains is in the SET MENU > MANUAL SETUP > 1 SOUND MENU > A) SPEAKER SET, set your FRONT SP to LARGE and then under the LFE/BASS OUT, set it to FRNT (the LFE has choices for SUB, FRNT, or BOTH). Having the options setup this way will send all the bass out to your front L and R main speakers. If it doesn't sound up to your expectations after this, then you need bigger and better speakers with big woofers. If you are using a subwoofer, the 5760 manual suggests selecting BOTH to "reinforce low-frequency signals when playing back sources such as CDs".
However, looking at your Cerwin Vega VS-120s with the 12" woofer, you should definitely setup your Yamaha with LFE/BASS to BOTH. But remember, the Yamaha is still going to send some of the frequencies under 80Hz to the subwoofer so the only way to get the sub to stop working is to set the LFE/BASS to FRONT. You didn't say what your old receiver was, but if it didn't have a subwoofer, then your Cerwin Vega VS-120s were handling all of the bass and now perhaps you have a subwoofer added into the mix. If you don't have a subwoofer, then you should definitely set the LFE/BASS to FRONT.
This is what the subwoofer output is for though. I have a 12" JBL E250p (not the greatest sub but pretty good) hooked up to the 5760. I have my JBL E80s (which are not even close to the size of your Cerwin Vega VS-120s) in the front set to SMALL because while they do have two 6" woofers, they're not particularly made to push low-frequency bass (like the E100s which have two 10" woofers), especially seeing as their frequency response only goes down to 38Hz and 6" woofers aren't going to push low bass frequencies that well anyway. So by setting the E80s to SMALL, and having the crossover for the subwoofer set at 80Hz anyway, nothing under 80Hz goes to the front mains. For the LFE/BASS OUT, I have it set to only SUB so everything under 80Hz goes to the big box and I get plenty of bass with my CDs. If a CD isn't as punchy in the bass department as a 5.1 mix with discrete LFE, then I simply up the volume level for the sub until I get what I want, which is usually around +3.0-+8.0, depending on the CD in question.
I've experimented with setting my E80s in the front to LARGE so that the bass under 80Hz gets sent to them too, but it doesn't sound as good because I feel the E80s are now doing too much work in the low frequency ranges and it tends to make the sound "murky" and "muddy". Letting the subwoofer do the job for everything under 80Hz and allowing the FRONT SP to concentrate the mid- and high-range is what sounds best.
Or at least to my ears anyway. Your mileage may vary.
