It depends on what you're intending to make the hardware do. If the objective is to pull off as many signals as possible to route back into the DAW, you're going to want inputs galore...something like MOTU's more recent 24Ai, with 24 ins and zero returns could work here if the MIDI interface is being used for clocking and note signaling. But a more practical approach might be their 2408, as it offers 8 ins and (technically) 10 outs, with the ability to add 16 more channels of I/O via ADAT Lightpipe. Just keep in mind that both of those interfaces require the PCI-424 card...but then, that card ALSO has four interface I/Os, meaning that if you went with 2408s, you could wind up with 96 inputs and 40 outputs for fairly cheap. Plus, if you have one that has the PCI-424 card, you can then snarf up cheap 2408s that don't happen to have the card, making them all but useless UNLESS the card's present...ergo, cheaper.
But again, go and check the compatibility list I've linked above. MOTU hardware is only one option.