Here is a copy/paste of some information from the 1522k manual:
Originally Posted by pioneer 1522k manual, pg 94
SW - LFE signals and bass frequencies of channels set to SMALL are output form the subwoofer when YES is selected. Choose the PLUS setting if you want the subwoofer to output bass sound continuously or you want deeper bass (the bass frequencies that would normally come out the front and center speakers are also routed to the subwoofer). If you did not connect a subwoofer choose NO (the bass frequencies are output from other speakers).
-- If you have a subwoofer and like lots of bass, it may seem logical to select LARGE for your front speakers and PLUS for your subwoofer. This may not, however, yield the best bass results. Depending on the speaker palcement of your room you may actually experiance a decrease in the amount of bass due low frequency cancelations. In this case, try chaning the position or direction of speakers. If you can't get good results, listen to the bass response with it set to PLUS and YES or the front speakers set to LARGE and SMALL alternatively and let your ears judge which sounds best. If you're having problems, the easiest option is to route all the bass sounds to the subwoofer by selecting SMALL for the front speakers.
From reading this it seems what GregLee is saying may be true.
However, if so, then this would be a deviation from how brands like Denon/Marantz handle it. With my Denon if I set my fronts to large, sub to yes, and a crossover of 80hz, then the fronts will play everything and the sub will play stuff that is 80hz or lower. I would have expected Pioneer to handle this the same.
I would have to test this, but I believe that Pioneer does in fact handle it that same way. While I think GregLee's interpretation does fit into what the manual says above, I took a different interpretation from it. To me, it sounds like if you set your fronts to large, subwoofer on, and crossover of 80hz, your fronts will play everything and the sub will do 80hz and lower (just lIke the Denon). However, if you set the fronts to large, sub to plus, with crossover of 80hz, I think your fronts will play everything, and your sub will play everything 80hz and lower, but also it will try and grab some additional bass above 80hz. If you set your fronts to small, sub to plus, with crossover of 80hz, I think your fronts will play everything down to 80hz then taper off, and your sub will play everything 80hz and lower, but it will also grab some additional bass from the fronts/center above 80hz. Again, this is just my interpretation from eading this section. I have not tested it.
In other words, my take on it is that when your fronts are set to small, sub is yes, and crossover at 80hz, your fronts will play everything down to 80hz, but then it will start to taper off, but still play some bass below 80hz. The Sub will start at 80hz and play everything lower.
When fronts are set to small, sub to plus, and crossover at 80hz, your fronts will play everything down to 80hz, and not taper off below it. Your sub will handle everything from 80hz on down, but it will taper off going above 80hz taking some stuff that the fronts/center would have played.
Again this is just a guess based off reading that.Edited by Goride - 4/1/13 at 5:37pm