OK, let's back up a little and figure out the facts of the original poster's needs:
First, I downloaded the manual for the Peavey MD series mixers off the Peavey website. Click here to get it:
Download peavey md manual.pdf from Sendspace.com - send big files the easy way
I highly recommend you read through it to help understand your tools and plan your recording.
As you can see, there are 12 channels and all of them have mic pres with XLR connection. Each channel also has unbalanced 1/4" line in jacks, and inserts which are labeled "out/in" on this mixer. On each channel you also have a 3-band EQ, and two auxes: one called "MON" (or "monitor") which is a pre-fader, pre-EQ auxiliary send, and another called "EFF" (or "effects") which is a post-EQ auxiliary send. Finally, there are the ubiquitous pan and channel fader controls and that's your channel input section. Fortunately, you do not "need" an external preamp as this would be redundant, and all you will need to power those Behringer C2s and the Sennheiser at the same time is 3 channels worth of 48v phantom power from a standalone unit as explained in my post above; I would suggest getting either a 4-channel phantom supply such as the Peavey PS4 (if they still make them!) or two of those 2-channel Samson S-Phantoms at 49 bucks a pop.
When recording the band and chorus simultaneously, without knowing more about your situation, they way I'd probably approach it is to use the C2s as a stereo pair on the band, the Sennheiser mono on the chorus, and use the SM57/58 for spot mics for soloists as necessary. Fortunately, in a venue of that size it doesn't sound like you have to worry over acoustic problems like wall reflections and should have plenty of latitude in your mic placements.
I hope this clears up your original questions-