Audio amplifier limiting output power!

[April155]

Hello, I hope somebody could help me . My audio amplifier limit output power and I don't know how to deal with it.
What I have:

A transformer rated at 150VA / 30V (center tapped) / 5A
Speaker rated at 30W / 8 ohms (measured 6.3 ohms with my multimeter)
Will use class AB amplifier:

LM4780
Question:

If I send +30V & -30V to this chip, I will get 45W at 1%THD+N:

Is it possible to keep +30V & -30V but limit the maximum power to 30W? Is it by playing with the gain (feedback resistor value)?

I read somewhere "...power amps at lower gains requires more input voltage to get the same power output, with the same speaker impedance".

How to adjust/calculate the gain so that I get a maximum of 30W output with +30V / -30V power supply?


Best regards