Again, from my experience, you will likely get the best looking frequency response by:
- Run Audyssey for all 8 positions, follow their instructions to the letter.
On completion, go back and do the following:
- Set all speakers to small.
- Set crossovers for any bass capable (no much how capable) speakers to 80 Hz (in some cases, 90 or 100 may be better.
- Set smaller speakers that have F3 below say 65-70 Hz to 100 Hz or 120-150 Hz for small satellites.
- Set LPF for LFE to 120 Hz, or higher if you wish.
Some people like LFE+Main, but I am quite sure if those people would use REW to plot some FR to compare LFE to LFE+Main, and they prefer more accurate frequency response, they would go back to just LFE on a heart beat.
After that's done, listen to it for a few days, then you can experiment lower crossovers, LFE+Main etc., and see if you prefer the other settings, but that won't be for "accuracy".
No, it will make no difference because as soon as you set running Audyssey, the volume will automatically be adjusted to produce about 71 to 75 dB of SPL at the main mic position. You cannot change that at all.