curt,
I just did an install with an MSC-400 and HR20-700 controlled via rs232. I used the IOGear USB to serial adapter and it works perfectly.

Note that the HR20 serial control only works at 9600 baud. Also, the MSC-400 serial database does not have an entry for the HR20, so you will have to create a new device and enter the commands manually. Use the document listed previously in this thread to get the rs232 commands.