I guess the 5-pin jack is just much tighter? I tried this morning and was able to get it in there by just pushing harder than I thought I would have to. I'm using the GCP with an Eleven Rack. I'd be using the Midi In with my PC for programming. Maybe. I was able to get quite a bit setup last night just using the GCP itself, so I might end up just doing everything there. Thanks.
If, as you said, you're using your GCPro with an Eleven Rack, you should check out the Ground Control Pro + Eleven Rack
Expansion Pack sticky at the top of the page...