Not sure if that makes sense unless your going for ATMOS / DTS-X.

With only bed speakers the surround processing will assume a non-object format. So, I don’t think the LFRS will improve your experience, over the QS10s, given that you want a diffuse image in those formats.

Now if you are going ATMOS and also adding tops … it’s still an experiment … as I’d postulate that 95% of the time movies are going for diffuse surround and you’d at least want sides and rears to get it. I’m also unsure if you’d get the actives to Image well with the 660s to give you great object placement for the other 5%.