I agree, the snap toggles with a stud should be fine. If you have a mechanical engineer as a friend, you can confirm with him. But, yeah, I was gonna mention this as well. HD has several types of anchoring mechanisms for attaching heavy weight to drywall.
The other option I like, is attaching a 1 by or 2by across your three studs, and mount to that. That should still be hidden behind a 55" TV.