My current HT:
I tried to measure the Rythmik FV25HP at where I had the JTR Captivator 4000ULF.
The key is to have the acoustic center at the exact same location.
I reran Audyssey with the following settings on the amp plate:
LFE in, Limiter On, PEQ Off, Lowpass filter @ AVR/12, Extension filter @ 12Hz low damping and Rumble filter: On.
I read that these settings provide the most tactile response (perhaps at the expense of extension).
Then I added 3dB to sub level and did the sub distance tweak. I did not change any settings for REW.
First, center channel Audyssey on (red) vs. Audyssey off (green):
The Rythmik FV25HP provided solid extension down to 11Hz in my room.
Sub only, Audyssey on (orange) vs. Audyssey off (blue):
Again, solid extension down to 11Hz.
Audyssey on, center (red) vs. sub only (orange):
Finally, main volume @ -8, center (black) vs. sub only (purple):