Resurrecting this old thread. I have a Time Traveler and a Holoseum cabinet (probably one of the few collectors with both?). Game play on both games is really poor, but they sure are oddities.
I have the external audio amp as well. But I would guess that something like this would also work. I tested the board and it works fine
http://www.amazon.com/gp/product/B007TUSXEY/ref=oh_details_o08_s00_i01?ie=UTF8&psc=1
I used one in a Pacman cocktail MAME project...
Are you still looking for this? I actually just pulled one of these out of a cabinet that was converted to a Lethal Enforcers. I'll get it on the test bench this afternoon to make sure it works.