After 3 tries with Audyssey, my subwoofer trim level is still at -12 dB (other speaker levels are in -5dB to -8dB range).
I already did the 50% volume level, direct input and other recommended settings for the sub. I don't however, use a tripod or microphone stand. Hehe.
I read in one of the FAQs that the subwoofer level should ideally be in the +- 3.5dB range. Can I just set it to that?