What makes you say the Aisin fluid is crap?
Based on the Mazda forums I browse, any ATF which states compatible with the Mazda FZ fluid should work fine: Aisin, Castrol, Valvoline, Shell, Mobil etc all make compatible fluids.
There's also a guy who runs AC Delco Dexron VI (with lubeguard additive) in his 6...he's done so for well over 100,000 miles...
It's not crap Aisin trans fluids are blended by top suppliers.