I've moved to doing surround recording and monitoring has been the retriction to post processing the recordings well. The motivation to pick up the second pair was primarily to have 3 identical speakers across the front (L,C,R). Most of my surround recordings are 4 channel (Left,Right,Center,Back) with a single channel of surround information. For now I just mult that Back channel to multiple speakers around the back and sides, which works suprisingly well for general hall ambience and audience applause.
Once I get into processing these recoringds I plan to look into ways of decorelating that single Back channel into 2 channels for typical 5 channel playback. For that work it would be great to have 5 so they would be identical all around. I don't think it's that important to have the same speakers around the sides & back for enjoyment listening, but for tweaking the raw multi-channel recordings into something finished that translates elsewhere well, I think it would be benefitial.
The room is setup on a diagonal and I've put the 4th 802 in the center back, between pairs of B&W surrounds and Klipsch KSB 3.1 bookshelfs wired in parallel as Ls & Rs.
I power them all with a 7-channel Panasonic SA-XR55 class D reciever for the time being, which sounds much better than it has any right to, and switches to a bi-amp mode for stereo. I'd like to improve that, but I know the room will benifit more from some bass trapping.
Funny you mention the ambisonic decodes as I just picked up a Tetramic last month. I've not decoded any surround playback from it yet, only realtime stereo decoding of the raw files directly out of the VVmic software (which is really ear-opening to play with). Of course now I'm burning to hear a full ambisonic decode so I may shift things around. I also have a few recordings I've made with 4 omnis spaced across the front of the stage that I'd like to playback with all four speakers in a row some time, just because.
I'm about to walk out the door to drive up to Merlefest in a little bit so appologies if I don't respond for a week!