couple things it could be the cap is going had it happen to a power acoustic cap then all of a sudden you got no bass because the cap went. any ways try disconnecting the cap and see if you can get volume out of it. at 500 rms you should not even need a cap it that small of a amp. i got 600rms hook to my Taurus but it a small drawl amp a kenwood excelon x10d drawing 40 amps. the most you should drawl is 60 amps. but those subs should hit with that amp but the other guy could be right to you will drawl more power at that exact frequency so if it tuned at 32 and it hitting 32 your going drawling more power. instead of them being 500rms they may take 6-800 rms got to remember caps are just a band-aids. i am not the best at boxes but is that tuned a little low shouldn't it be tuned some were in the 35-47 hz range? got to remember if you go 30 hz your on the verge of not hearing the bass but only feeling it in a ported box. because any thing 30 hz and below is out of our hearing range and if you turn the ifs or subsonic filter on it my cancel out or not play it. your not saying muddy so your cross over point is not wrong. or it is one of the two.

I don't think that the tuning frequency is the problem if that IS in fact what it's tuned to. A box tuned that low will still play higher audible frequencies, besides the tuning and box were both the same as before when the stereo was bumpin' in the first place. I did mention and agree that the cap should be looked at though.