This was an interesting thread to read about.
I have a Viking 910 and was about to go crazy and throw it out into the parking lot of the dealership. Then I decided since I was going to throw it away anyway, I started taking it a part to clean and see exactly what the threading was all about. Someone mentioned to unthread it and keep re threading it until it is easy.....which is exactly what I did. It is not pleasant, but I can do it now. I keep neutral threads, grays, ecru, in it so I don't worry about the colors each time.
I think what was giving me the most trouble was the thread wasn't "clicking' properly into the tension disks. So even if it was threaded right, it wasn't sewing properly and just naturally I blamed it on the loops and hooks. So make sure it snaps into the tension disks and take control. You own the machine.....not the other way around.
Good luck and try to find the manual, or something on youtube.