I had no issues using Parallels and SmartCAT. I was using fldigi, though I don't think I would have had any issue using wjst-x as it was just another application using CAT like fldigi. The only issue I had was with the transmit signal in psk and afsk. Didn't try any other digital modes on transmit.
Have you tried asking the people who write and support Parallels? I get on their website and have asked questions regarding issues and I usually get a response within 24 hours. I don't have the extended service but they will respond to questions posed on the web site.