I flashed the MA6 firmware only into my cm10.1 sprint galaxy s3 wihout having to go back to stock, working fine....
Used CWM 6.0.2.3 recovery
here is the link to the site
[ROM] 2/13/13 Sprint Touchwiz Jelly Bean 4.1.2 (L710SPRBMA6) Odex/DeOdex - xda-developers