How do I choose the power rating of resistors in audio power amplifier?
110 watts into an 8 ohm load implies an RMS current of 3.71 amps. That current, through a single 0.22 ohm resistor implies a power of 3.025 watts. Considering that this power is shared by 4 resistors, the average power per resistor is 0.76 watts.

But then one has to also consider the biasing of the output stage and this will cause a certain amount of DC current to pass though the resistors so maybe 1 watt per resistor might be dissipated if it's a class AB stage and possibly a couple of watts if it isn't properly biased i.e. it is closer to a class A stage.

The zobel network (C16 and R33) on the output might also add a few tens of milli watts to each resistor at lowish frequencies and a few hundred milli watts at high audio frequencies.

So you could be looking at maybe 2 watts to 2.5 watts for each resistor and therefore choosing a 5 watt resistor seems like a little bit of overkill considering that I would opt for more like a 3 watt resistor.