So instead of running more controlled experiments with regards to my quad setup, I ended up with a quick and dirty dual MS rig out in the field this past week.
The rig consisted of a pair of schoeps CMC6 bodies with the Fig 8 capsule and the hypercardiod capsule making up the front portion, and a Line Audio CM3 rigged up for the rear M all inside of a big rycote blimp. The schoeps mics went straight into a 744t 1-2, and the CM3 went through a sound devices M1 and into the 744t channel 3.
The whole rig fit into the rycote blimp very well, and when I took it out of doors the blimp still provided great wind protection to all three mics, since non were very close to the edges. I generally monitored the schoeps rig decoded, but sometimes listened to all three mics in mono.
I took this rig to a local hospital to record ambiances for a documentary that we are working on. I came back with about 3 hours of recordings from a half-day all access shoot, and got some really killer stuff (including a real live surgery).
I protools I decided to align all three tracks and mute them. From there I sent the Schoeps MK41 (supercardiod) to bus 1 prefader, the Schoeps MK8 to bus 2 and bus 4 prefader, and the CM3 to bus 3 prefader.
I then set two stereo aux inputs up - a front one fed by bus 1-2 and out to LR, and a rear one fed by bus 3-4 and out to LsRs - both with Waves S1 Imagers on them set to decode MS.
I was shocked at how good it all sounded. Maybe some of the best recordings I've made in my life.
Imaging was spectacular throughout, the balance of direct to reverberant sound was excellent, and that $150 CM3 played so nice with the crazy expensive schoeps rig you'd never guess the price of that thing. I didn't find the time differential between the CM3 and the schoeps MK8 capsules to present much of a decoding problem, probably because most of my sources were ambient and were sending as much reverberant sound to the mics as they were direct sounds.
Summing all three decoded mics to mono caused zero issues. Summing this rig to mono effectively removes the Fig 8 mic from the sound, leaving only the sum of the schoeps mk41 and the Line Audio CM3. Given that they were both aimed in opposite directions and recording ambient sources, the non-time alignment didn't do anything particularly strange or phasey. It's possible that time aligned capsules would lock together even more tightly, but the 2 inch or so differential was insignificant in this specific setup.
This is without question a killer rig to take into situations where you need to capture lots of surround ambiances while on the move. I think I still prefer the spaced mic technique sound to this one when I have to luxury of setting it up and not having it change the vibe of the ambiance I'm recording, but honestly I only prefer that technique over what I got here a little bit. Things didn't feel as "narrow" as they did in my initial dual MS test, and the use of the same fig 8 on both ends really locked the image down tight from front to back.
Color me impressed. As I go through and edit the recordings more closely I'll find a couple of nice bits to post up of both the front and read decoded recordings.
update: here are some choice decoded sounds from the shoot: