I'm curious to know what you consider "very loud aggressive music.
Lately I have been listening quite a bit to Fear Inoculum by Tool. I also like Orbital, NIN, Ministry, Big Black, Moon Duo, The Black Angels, Foo Fighters just to name a very small sampling, along with other genres like Folk, Jazz and classic Country.
And 4X 12" subs? What is your crossover
My main speakers are book shelf speakers, so two of the subs are slightly behind but in line with those, and those subs are low passed at 161 Hz using a 24 db Butterworth slope while the mains are high passed at 191 Hz using a 24 db Link/Riley slope which gives me a 6 db down point a little under 200 Hz. The actual down point and frequency will vary somewhat depending on the gain settings for the front subs and mains which varies from recording to recording. The other two subs are placed in an asynchronous (not the word I want but the only one I can think of right now) pattern in the room and are high passed at 79 Hz using a 48 db Butterworth slope. All four subs are high passed at 34 Hz using a 24 db Butterworth slope.
Are you feeding them with sub-outs or speaker-level?
My preamp connects to a XTA DP448 speaker management unit that handles the crossover duties, time alignment, gain setting, driver protection, and per channel input and output equalization if desired. I will never again use a speaker level sub connection.