Martin,
I've been trying to find a good commercial IR to Serial Port interface, so far the best one I have found is at Actisys (below link). It is kind of pricey at $59.00 but it sure looks good, and I think that I would be willing to pay that for the device if there was some software to support it. Maybe another MX-500 owner knows of a cheaper one.
Good Luck,
Duane
[Link: actisys.com]