Had a couple inquiries as to what can be used since I posted
http://forum.hauptwerk.com/viewtopic.php?f=15&t=16099&start=15#p120998. Simply, if your MIDI decoder can drive 3 - 5 volt LEDs, it most likely can drive a 5 VDC reed relay such as any of these
http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR0.TRC0.H0.TRS5&_nkw=5V+Relay+SIP-1A05+Reed+Switch+Relay&_sacat=0. If needed, you can use such a SPST relay to drive a larger relay to do more involved tasks.
Rgds,
Ed