Dear OMs!
I think that with correct combination of VAC, VAC repeater and virtual COM port pairs all is possible.
You dont need any phisical connection to radio. Modem can be connected to PC sound card. But you have to use VAC (VAC repeater) to send modulation data to SUNSDR2DX.
Radio is not a problem.
You didnt try enough. I dont have high cost PACTOR
modem to try it by myself, but all digital modes are working and I dont see the reason why PACTOR mode even with external modem is any diferent.
The easiest way is to blame EE company (which by the way is doing excelent job) and SUNSDR2DX HW.
Regards with high respect!