Beleive it or not, some bass blockers can actually INCREASE bass. You may not believe me, but i have charts and proof in books if you need to see for yourself. Adding an amp to anything will always make it sound better. I would say take your bass blockers out. Wire each speaker on a seperate channel into the HU. You should usually never bridge a head unit like it sounds like was done in your case, then play around with the fading and balancing and level controls on the HU and see what you can get.
Try this out and see where that puts you. If you are still lacking, an amp may be in your future....
'84 Chevy K5 Creative Conversions Blazer (super rare!), restored, new paint, new 355, dual exhaust, interior in progress
4-Boston RX7 5.25's
2-Boston RX7 6.5's
2-Shocker Super Extreme 12's in 11 ft^2 @ 32hz
Soon to come:
US 2000X or Tsunami 1800
7 inch screen
PS2, DVD player, VHS player
Hope to be done around the 1st of the year!!!!