If you can play games then its not the Z80.
Personally I never saw a bad YM2610 either...
So, it could be;
1) bad volume pot
2) bad electrolitic capacitor around sound region
3) bad amplifier IC (most probably)
4) bad speaker wiring?
When you play with the volume pot, do you hear at least a hum or a hiss sound? Or if you tap the capacitors with your finger do you hear anything?
During the above simple tests, if the PCB is still dead silent then most probably the amplifier IC is fried...
As yavuzg said you should check that things ... but if you're getting humming/hissing going louder/softer when you turn the volume up/down with the pot the power amp HA13001 should to its work, by the way you already replaced it and the audio issue is still there.
if something in the digital part of the audio circuit was bad the startup test should rise at least a Z80 error, so you should focus on the analog section of the circuit.
Look at the attached picture, the ICs in the yellow square are the DIGITAL part of the circuit, you should check the ANALOG part the RED bordered one.
The audio chain is the following:
(DIGITAL) Z80/YM2610 > DAC YM3016 (DIGITAL-ANALOG CONVERTER) > OPAMP uPC844g > POWER AMP HA13001 > JAMMA
So you should check the DAC and the OPAMP, they are light-blue dotted.
Which tools have you available for troubleshooting?