Sorry you're having issues with the Pfaff. I have no advice that you haven't tried or been given. I can only say that when my machine kept breaking new needles, I took it to the shop and the repairman said there was a burr on the race. Couldn't be filed down, had to be replaced. It was a $30 part plus $100 labor.
As for a great machine for FMQ, I love (!!!) my Janome 8200. It's really smooth and has an 11" throat and I've never had a tension trouble.