Not sure if this will help since we are stuck in the 90's with our laptops but to talk to a DMC we have to use a 485 converter and run a program that switches to 485 comm on the laptop, then switch back to 232 before using IMS or something (It's a PITA, the FAST tool is priceless.) What program are you trying to run for the DMC? As far as a general USB to serial converter, the Triplite Keyspan is the only one I've found to work consistently. I use it with a terminal emulator on my Mac to watch live logfiles on CPUA's and CGA cards. Hyperterminal on that old laptop is too slow to be useful.
