I have some problem with my audio amplifier, and I am not sure how to continue with my calculations. I would like if anyone can help write me the right equations that I need to make.

Here you can see the circuit (which I took from "Art of Electronics"), but in my case I have a 8 Ohm load which affects my circuit in a way that the output voltage is cut.

I can experimentally set some values that can give me a solid output, but I would like to know exactly how to find problem in this kind of situation and what should be calculated with what equations?