What kind of power are you running to them? If you're clipping them because of not enough power, they may distort at all volumes, but you'll only be able to really tell at the lower frequencies...
The most I could go is 32" wide 16" tall..I have no idea how deep I can go tho because if it gets too deep with won't be able to slide in the trunk because you have to angle the box to get it in...I dont' know if that makes any since to anyone besides me though.
I would look at what you have now...that should be very, very loud...if you paid that much for the box and had a guy install them that didn't know alot, there's your problem...not the subs or power....
I installed them. They are wired at 1ohm...the box design might be the problem but I'm not going to be able to get much bigger...if at all. I seriously think the subs are about to blow and my car just ***** for loudness.