I didn't get my answers properly highlighted so I'm giving it another shot as well as fixing a couple of mistakes from my original post:

What Axiom subwoofer(s) do you own?

Yamaha YST-SW315

Where do you have the Level, Frequency, Phase, and Subsonic Filter (if applicable) controls set?

Level 7/10, Frequency about 120 Hz, Phase Normal - This sub has no Subsonic Filter and likely produces no significant output below 20 Hz

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

RCA

What receiver/processor/pre-amp/integrated amplifier are you using?

Denon 4802

What are you using for your main speakers?

LFRs and VP180

Where do you have the crossover frequency and trim levels set in your processor/receiver for your main speakers and your Axiom subwoofer?

THX (80 Hz) but with fronts (L/C/R) set to Large

Are you using the trigger on your subwoofer?

Yes it has an automatic trigger that turns it on when a signal is detected on the RCA. This is set at "Low"