Lab tests by hi-fi magazines that do thorough reviews show that some AVR's distort the subwoofer signal when the sub trim is set to 0 or higher, thus many folks such as the SVS staff recommend setting your AVR sub trim about 25% of the way up from the bottom so you avoid potential signal distortion yet still have some room for conveniently tweaking the sub level on the fly if program material warrants it. So for example if your AVR sub trim has a range of +/-12, you would ideally set it at about -6 and adjust the gain control on your subwoofer itself during calibration with Avia or whatever pink noise tones you normally use to set speaker levels.
Receiver: Marantz SR7008
Source: Oppo BDP-83 multi-region, Sony BDP790 3D
Display: Panasonic TC-P65GT50 65" plasma
Speakers: five (5) EMP Tek R5Bi
Subwoofer: Rythmik F12