What gearing did you run? That 2779 KV on 5S is a ton of RPM (51411) and amp draw. Too bad, but I wouldn't be so quick to judge Quark on that. They make some very good products overall, and anything will fail if it's pushed too hard. I bet it was fun while it was working though!
A 6xl on 5s lipo!!! That setup can most likely pull 150 amps, if not more... No wonder the quark died. Try a 9 or 10xl next time. Conversion looks nice though, good job.