I just thought of a primo reason for 7 ch stereo. Tell me what you think of this!
Listening to mono Beatle LP's. Back in the early to mid-60's, mono was the primary mix and stereo mixes were not good at all. In fact it is pretty insulting to my ears to hear some of those stereo mixes. So the mono is highly preferred for the first 6 or 8 Beatle LP's. Thus, why not listen in 7 ch stereo?
Btw, one great, great record is Dusty Springfield's "Dusty in Memphis". It has a heinous stereo mix, so I made a new mono mix of the stereo mix from my computer.