Not enough Bass - who is to blame?

[zebracatzebra]

Before I start an expensive trial and error of finding the weakest link in my quest for bass I thought I'd ask for some advice.

So my setup currently consists of an Onkyo 606, Polk RTi A7 fronts, Polk CSi A6 center, Polk FXi A4 surrounds, and two Elemental Designs A2-300 subs and I am in a dedicated HT room 10x25x7. I am happy with how movies sounds with ground shaking bass, but when it comes to music the system really feels lacking to me. There just isn't that bass boom when the music hits the same way there is a bass boom when an explosion hits. I have my receiver calibrated with an SPL meter and the equalizer is set to manual with bass turned up higher that audyssey but it's just not doing it for me.

Any ideas what I should focus on first as the weak link? The speakers? Subs? The receiver? Add an amp (which involves a new receiver too)?

Pics are in my gallery and thanks in advance for any input!