Well, here's a short version, maybe I'll write more later...
There was a lot of people crammed into a semi-small space, and I ended up not really being able to direct the setup very much -- just didn't seem entirely appropriate (or totally feasible either, but there's a longer version of that story). However, that wasn't too much of a big deal, and at first listen the recording came out pretty damn good -- although the room was small, the acoustics were excellent with treatments on the walls and a carpeted floor, nice and dead/dry for recording.
So, I ran J-Disc omnis as my main stereo pair, and that was just awesomely transparent with a very good image. I then mic'ed the vocalists (who were to the left) with a single LD. The vocalists also sang into 2 SM58s that were feeding a monitor, which was a good and bad thing (the monitor helped me pick up the vocals a bit more, but it didn't sound as pure and the monitor had a slight hiss which was audible at quiet moments). I then had room for one more channel, so I put a card near the bass/vibes thinking they'd be the quietest on the stereo pair mix. After critically listening during the first 15 minutes of rehearsing the first track, I made three crucial changes. I had the guitarist turn up his amp a tiny bit, the violinist turn up his amp a tiny bit, and then I moved that extra card to be directly under the vibes only and away from the bass because I could hear the bass no problem on the omni pair but I couldn't hear the vibes at all despite his playing "louder than normal." Those minor tweaks, made a huge difference for the rest of the day, and I think the recording will serve its "demo" purpose quite nicely...
So, major thanks for all of the ideas guys, the brainstorming helped me be able to deal with the situation as it unfolded and it looks like it made for a successful recording (maybe even one of my personal best)!