I didn't look at the wiring of this machine, I assume there are 2 speakers? Have you tested the speakers at all? Measured their coil unplugged? You have sound, but it's low, does the volume control affect the volume at all? The voltages are good, no loud hum even if the volume is cranked up to max and you touch the input pin with a finger?

I see only 2 things that can happen if the amp doesn't make the loud hum, the input pin is pulled down from the volume control so low that it muffles anything coming from the input, but the pot and the amp have been changed to same results.

One of the 2 speakers, or both, are damaged and it is actually pulling down the output because the impedance of the coil has changed. From the schematic posted above, unplugging the volume control would make sure nothing is pulling down the input pin. If you don't hear a loud hum or static touching the pins then with the volume control unplugged, I'd definitely focus on the output stage.. The caps you changed included those? Maybe test the resistor values as well.. But check the speakers and measure their coil with resistance (ohm) on your meter.