Live audio & MIDI, MOTU & Tascam together?

[Sean Holland]

I will be recording a live rock band in a couple of weeks. (A first time experience!) The sound company that is doing the sound have very kindly offered to let me plug into their splitter. They will have a 3-way split: FOH, monitor mixer, and me! Totally cool of them to do it.
The computer is a PB G4 1.5ghz w/ 2 gig o' RAM. In the rack is an 896HD, and an Octopre connected to the 896 via light pipe. Also a couple of decent preamps (one of the preamp units is a Millenia HV-3C, if I might boast from my modest little world) in the rack, but they don't increase the channel count. Tracks will be recorded to a 120 gig Glyph in the rack.
So I have 16 channels in. Before the drums, the band will need 12 channels. The drummer uses an electronic kit and usually mixes himself and sends a single line-out to the mixer. I want to keep at least one channel for crowd sound, so at present I will have 3 channels to deal with the drums. I'm waiting to hear back from him about whether he can split his drums into mutiple discrete signals, but I'm assuming he can.
Anyway, I also have an old Tascam US-428 USB interface. It has a S/PDIF digital out. I was thinking of getting a box to convert that S/PDIF signal into AES/EBU so I can have an extra stereo input into the 896 (2 mics into the US-428, stereo out the S/PDIF into the 896's AES/EBU after running through a converter). I could use that for crowd sound and have 4 channels left for drums. Is this doable? Can I have light pipt (ADAT) and AES/EBU going in at the same time?
Another question: With this set up, would it be possible for me to also record the drummer's performance as MIDI through the US-428 at the same time as doing the audio recording? I'd like to do that so that if, during mix down, we find we want to put more oomph into the kick or whatever, we could use the MIDI of his performance to trigger appropriate samples.
Thanks for any input you might have.