It could also be the amplifier itself, or the power wiring that runs to the amplifier.

You say that it plays fine with the volume quiet. That tells me that it's a power thing (turn the volume up, then more power is needed). Does the amplifier have a power indicator LED or a limit/protect indicator LED? See if those turn on and off when the audio cuts out.

Does the empeg show any strange behavior when the audio cuts out? For example, does the empeg screen go blank or show the battery icon on the screen?

If not, then I'd definitely consider that there is either a loose wire, a faulty amplifier, or a wiring problem with the power lines that run to the amplifier.