I had the exact same thing with my Iron Maiden premium. The sound was horrible. I too got a replacement node zero board. No change. Sound clipped horribly and was awful turned up.

I worked on a Total Nuclear annihilation and a Houdini. I was very impressed with their sound. I ordered the same amp.

ONEU Audio Amplifier, Separated Subwoofer Volume Controlled Stereo Amplifier 2 x 45-Watt and 1x68W Sub Output, Super Bass 2.1 Channel Audio Power Amplifier with Power Supply .

I made cables from the line out into the amp, and cables to plug from the outputs to the stern speakers. I added flipper fidelity speakers as an upgrade.

It's a night and day difference! Sound is clear and balanced between the backbox and cabinet. Gets too loud even for a 50 something Metal Head. Highly recommended!

I made a couple of custom cables. I made a splitter to get switched 110 off of the Bill Accepter harness for the amps power supply. Then I made a line out harness for the audio. Molex .100 to RCA. Also made harnesses to plug directly into cabinet and backbox speaker harness.

I fix pinballs for a living, so I had all the parts just laying around.