There are adapters available which will let you add serial ports via the USB plugs. Although I've never heard of any Empeg owners trying an upgrade with one of these adapters, I assume it would work. Does anyone have (a) experience with these, and/or (b) links to these products?

It does work. However, if the legacy-free PC has a free PCI slot, you should look for dual serial port PCI cards -- they can be cheaper than USB-to-serial adapters.

Peter