Incidentally the TF-80SC is heavily used by Volvo (as well as many other marques) and available in the S80 D5 Auto, which is 440Nm in stock tune, technically the box's limit, yet Volvo are able to mass manufacture and distribute with a limited failure rate, which is testimony to the box's strength.
Moving to a manual box would let you go with a much stronger racing clutch, solid mass fly wheel and quaife differential, which theoretically would handle the extra torque, but putting that much power down from standing is going to make for a very quick 1st-2nd-3rd gear change
The TF-80SC has 6 x clutches, one for each gear driven by the solenoids, and designed so that one clutch hands off to the other with overlap for smoothness of power transfer so it can change gear much faster than a human could.
This seems an infinitely better option to put down the extra power efficiently as far as I can see.
Update on the potential upgrades:
don't make an upgrade kit for the TF-80SC, only standrad spec replacement parts so they are a no go.
Are able to re-jet the valve body to allow more pressure to be sent to the clutches, which will in turn give them greater holding strength and more torque handling ability. They do not supply the parts, only modify your own so you would have to send your valve body to teh US for the work to be done.
I am still working on solutions, but thought I would offer an update so far.