Recording a choir (over existing tracks)

I need to record 12 singers at once for a church band recording. The song is "Sanctuary" and they'll be singing to pre-recorded acoustic guitar and violin tracks (a pretty sparse arrangement - the vocals will be the highlight). My concern is how they will be able to listen to the tracks while they sing. I only have 4 jacks on my headphone amp. I was thinking of these possible approaches:
 
Plan A - Just have 4 singers listen to the music on the headphones. The rest of the singers wouldn't hear the music but would hopefully be able be able to follow the other singers. If not...
 
Plan B - Have the singers listen to the music at a really low volume so the mic's didn't pick it up too much. I found this thread and it is discussed phasing issues. It's a pretty old thread though so if anyone has any updated techniques in Sonar or more to add to this issue, please let me know. If this approach picked up the music too much and/or caused phasing problems...
 
Plan C - Record the 12 singers in 3 groups of 4, so everyone has a set of headphones. However, we'd really prefer to get the cohesive group feel of them all singing together...
 
Any advice / suggestions?
 
Equipment: I have a fairly basic set-up - I'll be using 3 condensor microphones: A Blue BlueBird, a Rode NT-1000 and an AKG Perception 220. The BlueBird will go through my PreSonus Eureka pre-amp into my interface. That's my only dedicated pre-amp, so the other two mics will have to go directly into my Lexicon Omega interface. So I'll end up with 3 vocals tracks, recorded with Sonar 7 Producer.
 
Thanks!

How good are your singers' pitch? If you give them a few measures of reference music (over speakers), then mute the music & give them only a metronome, can they stay on key for the duration of the part?

That's how we did it once when headphones were causing a problem. It was only 4 people, but the strategy should be the same. I think a choir should be as open-air as possible, letting the singers do their natural thing, listening to each other in the room as they were trained.

So I would go with sortofa plan B strategy, muting the music when they start singing.

My thoughts would be:

A:  Get more headphones and amps if I think this might come up again.

or

B:  If this is the exception and not the rule....I'd probaby have a go at giving out as many headphones as possible to those who feel they most need them.  In addition, I'd pipe the score through some speakers so that the others could not only hear their counterparts singing - but a bit of the music as well.

I'd be very careful to keep the volume of the music as low as the singers could stand it...hopefully keeping the signal (voices) to noise (backing tracks) ratio as high as possible.

I'd also have second thoughts about using more than a stereo pair of mics on a group as small as 12.  That third mic could be a real bugger in the mix if you've got any bleed from the open-air back tracks.

There is a way to do this and it works very well. But you will get a mono recording. You set up a microphone in figure 8 pattern and put half the singers on one side and the other half on the other side.

You also set up two smallish speakers (on stands at the same height of the mike) either side of the figure of 8 mike (exactly same distance) pointing into the null points of the mike. (so the speakers axis and the singers axis are at 90 degrees) You feed the music in mono into the two speakers and also reverse the phase of one of them.

The singers either side of the mike will hear the music easily. It can be quite loud even. But you will be amazed at how little or even no music will be on the mike channel. The reason is the speakers are pointing into the two null points of the figure 8 and also the out of phase speakers produces a very weak centre image where the mike is.

Add a little stereo reverb to the mike channel for stereo effect. Or you can do a modified Blumlein setup except change from 90 degrees to about 30 degrees. That way you will still get great null points and some stereo information.

I have used the technique for singers who just dont like headphones and also for recording a large group of children singing to a backing track. Try that sometime! If you are doing this for a vocalist, keep the instruments in the speakers simple eg drums, bass and piano leave out all the frilly stuff! Also click tracks can still be used too just be careful as to what the click sound is. Limit the frequency range being fed to the speakers (eg 500 to 5KHz) Vocalists love this by the way. You will almost certainly get a better vocal performance every time doing this. It is more like a live gig! Headphones can sometimes isolate singers away from the music. Many famous people we know and love record their vocals this way.

The only thing to watch here is that the room needs to be fairly dead. (or very large so reflected sound is low in level) Otherwise the music will bounce around and end up being picked up by the mike.

You can also use two mikes in figure 8 to record a singer playing an acoustic guitar and get nearly total separation between the two. (I might have to draw that setup because it is one of those 'a picture equals a 1000 words' situation.) It is easy to underestimate the power of the figure 8 pattern. Its ability to reject sound coming in at 90 degrees is very very good.

I will tell you a little something based on past experience doing this. You'll be lucky to get everyone together in the same room at the same time and all lined up and singing halfway decently. Whatever other smallish technical details will be overshadowed by all the other baggage that goes along with trying to record a bunch of people all standing together.

I would just set up a small PA system (or whatever you have to play back music) and keep the volume as low as possible and let them sing to that. If you try to give everyone headphones you are just setting yourself up for heartache because this is not how they usually sing and the singers will go nuts trying to hear themselves and each other in proper perspective. Yes there will be a little bleed but it shouldn't cause a problem when mixing if you do it right. You'll have worse things working against you like paper shuffling, coughing, sneezing, jewelry rattling, cars going by outside, air conditioner noise, the janitor beating on something down the hall, etc etc etc.

I hope none of those things happens to you!! Good luck!

PS - how you have the choir standing is important too in relation to those 3 mics. It can be a little nerve wracking to get it right - especially when you've got a lot of distractions going on around you.
 
PSS - just another little bit of ad-vice: 12 people all milling around between songs will make your life miserable if you don't pay attention to cable dressing. They will see cables on the floor and it's almost like an invitation to step on them or walk on them. They can't help themselves. Get yourself as far away from them as possible (another room if possible or as far back as possible). Get a mic snake or at least some very long mic cables. Extension cords. A talkback mic for you. Duct tape!!

You could use an inexpensive FM transmitter, the type you would use to transmit from an MP3 player to a car radio ($20-$30).  Usually they use about 4 different radio frequencies.  Set it up on a send and have choir members bring in MP3 players that have FM radios on them (most players have them) and tune them to the broadcast frequency you selected.  I don't know about the I-Pod things have FM radios in them, but my MP3 player has FM.  I think it might be worth a try.