Here in the UK there are Chinese drives that supposedly handle 7.8Amps but its not much of an increase. Not really sure what others are out there, maybe someone else will chime in with info and reccomendations.
I think there are a few guys using the geckos and the sigmas/superiors, in fact I am sure JohnS is using the Geckos with the same motors on his Beaver mill, might be worth giving him a PM.
Hood