Just get JL W7 8" subs. Two of these will outperform the 4 x 8" subs you were using before. There is only one other 8" sub comparable to the W7, and that is the SoundSplinter RL-i 8", made by TC Sounds, but currently not available(on deep backorder). Or go with 4 of them if you want to damage your hearing. You can buy the W7 8 subs for about $250 online from discount sources. Note: the W7 8" produces more linear displacement in reality than most conventional 12" subs. You need to feed them 500 clean watts each (continous rating from amp).
-Chris