because NP is the Best.
Neilpryde Racepro is a very very stifftop mast, while X9/X6 has a very soft top, totally contrary. Don't rig a new x6/x9 recommand RS on a racepro please, maybe a shorter mast would just work out. Or a 430 base 400 top from a racepro.
In small sizes up till 6.7 RSR I see a lot of riders using X9 wave mast, these don't break @ all, but yet top-end perfomance. On bigger sizes you have to take the right mast, sometimes you can soften up the rig by taking a shorter x9.
A X9 in a RS slalom will bring the sail to the highest level, the 430 x9 wave... the best. X6 430, very good, no breaking problems.
Maverx? Maybe it works?!? Haven't tryed it. If it is more stifftop it will have a higher chance of breaking, and performance will be worse. Note: same factory = Not same mast.