I have a STR-D611. When I was in college I ran the DBFB all the time.
It was sick, d00d!
According to this
, DBFB is Dynamic Bass Feed Back. (Funny, if I were doing the marketing for audio equipment I wouldn't create a gaper gimmick called "Feed Back".)
It seems to strongly boost very low bass, much lower than the BASS EQ knob. I don't use it much anymore, except for action movies, because to me it seems to muddle the upper midrange, especially in the range of human voice (vocals and spoken word), trumpets, and some guitar solos.
I suppose the question becomes: Upon listening
, do you
music a) with, or b) without DBFB?
I used to like A. These days I like B. More balanced, methinks. IMHO. The low-bass "THX Bass Woofer Cooker" mp3 that's going around is fun with DBFB on.