Vinnie,
The tape inputs on these mixers are typically 10 k or greater, so that's where he should be plugging in the iMod. The mic inputs are typically 1.5k or less, and the remaining TRS stereo inputs are also typically about 10k -- but he'll need a cable with a 1/4" TRS on one end, and a pair of RCAs on the other to connect to the xbox (assuming the xbox has RCA outs.)
Other than that, I think it's pretty straightforward as the tape inputs are typically the same as any audio preamp.
-- Jim