I also have the Pfaff Grand Quilter 1200 with the Grace Next Generation frame and the stitch regulator. I've had it for about 2 1/2 years and use it a lot. This week I have done 3 quilts on it and am about to load a fourth. I'll admit that I had a little trouble with thread breaking until I got the hang of it and "found my rhythm" so to speak. Now I rarely have a break (and usually a new needle takes care of the problem) and I am not particular about what thread I use - I do a lot of double/queen sized for charity quilts so I use a lot of regular Coats & Clarks because it's cheaper and never have trouble with it. For invisible thread I will use Sulkey or YLI without much trouble. I use Schmetz needles - either quilting needles or just the universal type in size 80 or 90 so I guess I'm not particular about the needle either. Of course, every machine is different even when they are the same model so you may have a tempremental machine but I just wanted you to know that this machine can really be a workhorse. The only thing I don't like about it is the small throat space that means I have to turn those large quilts around halfway through. I wish I'd gotten one with more throat space but I hope to move up to that someday.
My only suggestion is to have the machine cleaned if you haven't already done so. It will really collect a lot of lint. I have mine serviced about once a year to clean out what I can't reach. Every time I change the bobbin, I use a small paint brush to really clean out the bobbin case and surrounding area, under the plate that covers the feed dogs, around the the thread guides above the needle, even on the presser foot. You will be surprised how much lint gets in all those places.
I hope we've all been of some help to you. Good luck with your machine and I hope you get it figured out.