I think a double output config will help, as the transductance doubles. This is slightly negated by the fact that the bias though each of the output device is only halve of the total bias current and the gate capacitance is doubled...
I will try doubled output pairs (unfortunately my speakers are 4 ohm). I think I could try lowering a supply voltage to +-15V and biasing one pair at 1A.
Is the puting all transistors on the heatsing is a good idea regarding termal stability?
Regards