I'm not too keen on stringing above 28 anytime soon, but why are the mains higher tension than the crosses?
There's gonna be a few snapped strings in the process, even on quality machines with good grommets on the racket. 66UM already has some trouble with anything past 30, although that is on used and very used grommets
The main factor, the grommets. My go to string is Aerosonic at 31lbs. and have never had a problem with string snapping from stringing. However, I rotate and replace the grommets religiously. If the grommets are bad, no machine can save the string.