Driving an RL circuit with an audio power amplifier
1) this is basic network theory, help us by mentioning the voltage of V1, the 0.04 seems too low, I would expect about double. If the inductor does not behave in a linear way that can explain this.

2) the amplifier behaves as a voltage source, at a given voltage the current decreases as the load impedance increases. As power is voltage times current, a lower current (at a constant voltage) results in a lower power.

To maintain the same maximum power at higher load impedances the maximum output voltage of the amplifier would need to increase. It is possible to make an amplifier capable of doing that but it would be complex and expensive.

3) Figure out how much voltage you would need for that. If you only consider the 40 ohms series resistance then for 7 A you would need 280 V. This amplifier is not going to deliver that much voltage as it is designed for much lower impedance loads.

Where to get an amplifier that can deliver that is a shopping question and off-topic. My bet: if you can find one it will be expensive.