500 Watt Audio Power Amplifier

What can be done to increase available audio power amplifier? The answer is either decrease load impedance or increase supply voltage. The lower the impedance, the more current is needed, making the construction of low impedance output stages more difficult (there are some other practical limits), so lets increase supply voltage!

Components/parts list :
R1,R11
47K
R2,R3 33K
R4 1K5
R5,R7 2K2
R6,R8 100R
R9,R10 56R
R12 820R
R13 10R/5W

C1 220nF
C2,C3,C4 100uF/100V
C5,C6 100pF
C7 100nF/100V

D1,D2 IN4002

TR1,TR2 D438
TR3,TR4 B560
TR5,TR8 A958
TR6,TR7 C2168
TR9,TR10 C2922
TR11,TR12 A1216