I don't use caps. I ported into the cabin so there would be no trunk rattle or the need to by sound deadening material, but the air never hits the 6x9 cones. the amp pushes 1141RMSx1 and pulls about 90amps off the alt. the stock alt is 120-140amps so eventually I will need another one, especially once I mount the 4 channel, since that will take an additional 40 amps, unless i upgrade it to the 600rms 4 channel.
Reason for the 2nd battery is the 2nd amp, new HIDs, new interiors and some other shit.
The overall system sounds great but I'm keepin the volume around 50 (with the bass @ -5 on the deck) to break in the subs (10-15 hours of playing time).
And, no, with this setup I don't experience/have wave cancellation. Its just like the setup I had in my 83 Caprice. No cancellation and much louder than firing towards the rear, but it all depends on the type of car and what kinda sound you're going for.