Since you've got multiple mics and an R4, I say go four-channel. Heh. I've been doing a lot of that lately and the recordings can rip. Considering you only have four instruments to deal with, you could actually mic each separately. But another approach would be to run two sets of stereo pairs. I'd get one pair in close, real close, on-stage if you will. I'd then put a second pair back and up high if possible. This will give you a load of options in post. You'll have that up-front sound from the main pair, but can mix in some of the room pair to bring in that live feeling of reverb and ambience into the mix. Also, it backs you up a little if one pair frys for some reason. Another approach would be to set up a stereo pair "like normal," and then reinforce where you might need more balance with a spot mic or two -- for example, if the marimba is behind everyone else, it might be cool to spot mic the marimba from underneath, then in post you can bring a little more marimba into play if you need too? Anyway, just some thoughts... Cause with that R4, I usually run fours mics in this type of situation EVEN IF I don't think I'll use the 3rd and 4th mics at all, hell, why not, you can always delete them, LOL!