What Axiom subwoofer(s) do you own?
EP500 (also a Polk 10" sub to be replaced by a second EP500 soon I hope).

Where do you have the Level, Frequency, Phase, and Subsonic Filter (if applicable) controls set?
Level 11 o'clock, freq is at highest (150Hz if I recall), phase 0, subsonic off.

How are you connecting your signal source to the subwoofer (RCA/XLR/High Level)?

What receiver/processor/pre-amp/integrated amplifier are you using?
Denon 4311CI for surrounds (I have a 7.2 setup), 3 ch ADA1000 for VP150 and M80s.

What are you using for your main speakers?

Where do you have the crossover frequency and trim levels set in your processor/receiver for your main speakers and your Axiom subwoofer?
I calibrate with Audyssey. LFE is at 120Hz. I set the M80s as Large. I leave the trim at the Audyssey setting for the M80s but bump up my two subs by 6db.

Are you using the trigger on your subwoofer?
No. I have had problems with it in the past.
--For every expert, there is an equal and opposite expert.