I have tried connecting my pactor modem to the radio directly via PTT, RX Audio, MIC. There is a latency that makes connections impossible. I tried with the !Long Path mode but that didn't work either. However, Robust Packet should not be a problem. VARA works fine in my setup. I don't have any issues with that.
Not being able to use Pactor with the SunSDR2 Pro doesn't worry me. I use it mostly for CW anyway.
Cheers,
Dave.