Routing Synths Using Apollo Console

[Jurupari Man]

This is more of an Apollo question than a Pro Tools one, but I'm at the end of a long day and my brain is fried. I'd really appreciate some help. I just picked up some synth modules and I'm having difficulty getting sound out of them through the Apollo console. I'm using a MOTU Micro USB MIDI interface, and have my MIDI keyboard controller plugged into it and MIDI outs to each of the synth modules. The modules indicate that they are receiving the MIDI (and they work - I ran them through a separate preamp first to test them. But once plugged into the line ins on the back of the Apollo, I'm not able to get any signal from them.