Flux gears wont work in a maxx.
Those appear to be the original 3906 diffs in an alloy casing, an old alloy casing at that ( note the 2 screw instead of 4 screw fixing pattern ). They wont last 2 seconds Im affraid.
Best bet for an overpowered heavyweight is the UE ultraLite diffs- check on ebay for 'supermaxx' or 'UE' / 'Unlimited Engineering'. You also have the option of FLM hybrid bulks + 1/8 ofna/ hotbodies diffs or the cheaper option of modding some Losi Muggy/ LST2 diffs to fit the maxx bulkheads.
The emaxx 3905 transmission is quite sturdy compared to the older 3906 version, though if you have all-steel gears ( UltraMaxxed ) then it would hold up brilliantly.
UltraLites:
http://www.rc-monster.com/forum/showthread.php?t=8012
LST2/ Muggy diffs:
http://www.rc-monster.com/forum/show...t=9153&page=15
FLM hybrids is the same principle & assembly method as the UE diffs basically, just that thr diff cases are built into the insides of the bulks.