Prior to converting to the 990/770, I was running a Denon 3800 for processing, it had a neat feature which allowed you to use a standard 7.1 speaker set but add a "b" pair of side surrounds "ostensibly for music" then select a, b or A+B surround modes. I have Dipoles on the sides and used a spare set of direct radiating towers placed in the rear corners of the room, well outboard of the rear speakers, for the rear surrounds.
I would often use the B channels only for music, particularly most classical as I felt that this gave me more of the hall effect than the front side surrounds. For movies, I started out using A surrounds only, but eventually gravitated to using the A+B mode for almost all movies.Both for the directionality and the improved bass for the towers. I would think that this would give the same sort of effect that Gonk is achieving by splitting the side surround channels.
With the 990/770 I accomplish this by using a speaker selector for the surrounds. bi-wiring the towers so that my selections are dipoles only, Dipoles + bass from the towers, towers only or the works.
This requires an spltter and an extra pair of speakers, but allows you to split of the 5.1 surround signals and still retain the capability of utilizing the 6th and 7th rear channels discretly when appropriate.