Unexpected huge MOSFETs power consumption
LTspice gives me hundreds of watts? I hope it's not relevant.

Unfortunately, it is relevant. You have shoot-through, i.e. current flowing through both transistors at the same time.



simulate this circuit &ndash; Schematic created using CircuitLab

Datasheet for BSZ520N15NS3
Datasheet for IRF9640

With the biasing resistors as in the schematic, significant current flows through the transistors even when the input voltage is 0.


By decreasing the 5k\$\Omega\$ resistors to 2k\$\Omega\$, the lost current became dramatically reduced.

There may be some cross-over distortion, but it is &quot;small&quot; for some definition of &quot;small&quot;. If this is for audio purposes, it might be audible. My own ability to discern &quot;high fidelity&quot; is rather weak.

However, I simulated at 5V, 2V and 1V, and even at a 1V input, cross-over distortion is not visible in the graph.