I'm not familiar with that particular machine. However, have you tried Jamie Wallen's technique for adjusting tension? It has helped a *lot* of quilters, and it works for all machines (even domestic). Here is a link to his Youtube video:
https://www.youtube.com/watch?v=Q1mRhcquZTM
What size and type of needle are you using? What thread? I have found Glide thread to be the easiest to use -- never shreds or breaks on me.
There are a couple of Yahoo groups you might want to join:
https://groups.yahoo.com/neo/groups/..._quilters/info
https://groups.yahoo.com/neo/groups/FunQuilters/info
Sometimes other users are the best source of help.
Also, when nothing else has worked, I have read of a few situations where the tension spring on a machine is worn out, defective, or positioned wrong on a machine. Worth a shot as a last resort.
Edit: Ditto on the quilt needing to be loose in the frame. Forgot about that, and it's probably the very first thing to check. It should not be tight. The rule-of-thumb is that you should be able to grasp a finger that is poking up from underneath the quilt, about to the first knuckle near the tip. The quilt has to flex a bit as you move the machine.