Hector Martin

Your 25k resistor needs to connect to out, not to the transistor bases. You have a controlled op-amp feeding an open loop transistor pair. The transistors need to be part of the loop.

Also the 100k input pot is meaningless unless you connect the third terminal to gnd. The opamp has high input impedance, so adding more has nearly no effect.

Yes, they act like separate blocks, but the transistors alone *aren't* a linear amplifier. They will heavily distort the audio without the opamp. And since they need the opamp they're no longer a separate block.