what subs to upgrade to?

ok so currently i have 2 jbl gto 10inch subs in a box that fits under the back seat of my 94 gmc extended cab truck... the box is roughly 1.3-1.5 cubic ft... not sure of exact size... both subs share common air space and are front firing... they are powered by a memphis 1000d... i have done some research on small enclosure subs and have found critical mass subs... http://criticalmassaudio.com/catalog/index.php?act=viewProd&productid=2 .. the company is a repitable company and the local shop has sold a couple sets so i know there good subs... my question is there any other sub that i should consider.. i don't have much more room to fit a bigger sub than the gto sub as they do have a rather large basket.. i open to all kinds of ideas so let me know what u guys think...S.O.B custsoms.. South Omaha, Nebraska

well we know the guy at local audio store rather well and i have bought plenty of stuff from him as well as brought him plenty of business.. so he slides stuff to me a lil over cost.. i think i can score the low profile critical mass.. for about 250 its like half off... i wish i could fit something like an eclipse titanium cause i would have w7s if i couldS.O.B custsoms.. South Omaha, Nebraska