Nice thread guys. most of the multi-pair mic stuff I have done was in addition to sbd to a multi rig, but I have played with the mics w/o the soundboard many times. here are my suggestions fwiw.
Use at least one pair of omni's in the mix because they will be less prone to phase issues.
Don't diss the x/y as long as you are close to the source. the advantage of the x/y is again the reduction of phase issues, and to my ears the image is awesome when on stage. Although I've never run m/s or blumlien, I understand that this is also an advantage of these configs.
I did an entire 3 day festival with a pair of ld's x/y center stage, split omni's 100' back, 15' split at the foh, a pair of cards on the stage corners facing the audience (only had one pair of omni's unfortunately and used them for the splits), and a stereo sbd feed. Most all the mixes were all 8 sources and I liked it a lot. Alternatively, the foh omni's mixed well with any of the sources once the delay was dialed in. Mixing too much of the stage sources however would drown out the vox so without the board it was a lot of omni but I like splits outdoors anyways.
The best 4 mic live mix I ever made however was indoor at a small venue. I had ld's x/y on center stage (centered to instruments NOT the geographic center of the stage), and two omni's on the outside corners facing the audience. I would do this again if I were to do a 4 mic live mix, and probably wouldn't try any other config unless the band had vocals. In a multitrack configuration, I would do the split omni's from foh or wherever was convienient and then add delay in post.
I ran heally one time FOB for MMW indoor as a 2chan and I hated it. Crowd was too pronounced. Applause nice and bright, and the music a bit muddy. On stage however this might be a good way to keep the instruments up-front over the drum kit in a drum center type situation, so I always thought I would try it again. I would be interested in how it works with a 4 mic mix, but my guess is it would be no big thrill.
So for anyone trying this I will suggest you try the center config on stage (x/y, m/s, or blumlien) and omni's on the outside stage corners at the audience if it is an amplified, non-vocal band. Or try a center stage pair mixed with splits from the rear/middle of the venue. It is my understanding that putting mics right on the PA cabs and mixing that with another source is a good way to go, but I have yet to try that. I bet that works wonderful when a band has vox and you can't get sbd access.
matt