Should i cross speakers over to "small"?

I have ht set up w/ the following: Yamaha rx1500, def tech 7002 bipols, def tech bpx2 surrounds(7 speaker system) and Def tech super cube II. I finished my basement and dedicated it to ht, room is 15 x 27, so i have speakers all set to "large". I like the 1500, but dont know if it has enough to handle what i have. Sometimes i dont feel the channel discretion....Would this help?
IMHO, yes.
You may be better off, much less strain on your receiver that way.

I had the same problem at one time (5 VMPS speakers plus 1 VMPS sub) and an under powered receiver.

My mains were VMPS Supertowers, the lower section of these are the large VMPS subs...Why would I run them small?

My receiver had pre-out for all channels so I just added a dedicated two channel amp to drive the fronts full range.

I set the center and rears to small and let the sub deal with their deep bass...this left the receiver with only 3 channels of 80hz and above work load....sounded fantastic.

You will need to do one or the other depending on your room and speakers I would say.

Following the advice of the expert who installed my Velodyne HGS-15, I set the pre/pro to shunt everything below 80 Hz to the sub, and it had the effect of really opening up my KEF 104/2s in stereo mode and enlarging the soundstage they generate. Integration with the sub is seamless, and you cannot point to the sub as a source of sound. I highly recommend letting the sub do what it does best, and freeing your other speakers of low frequency duty.

A different angle...
With all the speakers reproducing full range bass, woofers are in many places in the room. Standing waves and cancellations you didn't plan on may become evident. With all the bass coming from one location (the Sub) it's possible more locations in the room would sound better (instead of one sweet spot) Experimentation may bear this out. If all your speakers are indeed capable of reproducing down to 20Hz it could very well be an issue. It's even tricky with multiple subwoofers.
THX and almost ever professional group in HT recommend setting all speakers to small. Only in rare instances do we set the mains to large for HT.
The Answer is "experiment"
Your speakers are full range speakers with active 12" subs built in, correct? You should be able to get very good results crossing these over lower than 80hz. Because of the effieciency of your bass system here, You should probably try to cross lower. Yes, experiment and see. You may find they're very powerful and dynamic even full range, set to "large". If your receiver selects at different freq's, like 40,50,65hz, etc, you should try those. I would.
so far have set all surrounds to "small". noticed a huge improvement. Now looking at Adcom 7607 7ch to use w the Yamaha, waiting for local dealer to return call to see if will match up well w the receiver