Quoted from delt31:yeah this polk sub seems like the def go too. I already purchased and installed the pinball pro speaker and sub so I'll likely just keep that in the machine (maybe disconnect the sub) if I end up buying the sep sub. At this point, I'll buy one to try it out. Found a used one for 75 but I don't think it's a very good deal. Number of others selling them but not local and shipping kills it.
I had the pinball pros installed and hooked up a polk audio and it didn't work with both hooked up. I got no sound from the polk. So I ripped the pin pro sub out and rehooked the stock speaker back in and it worked. You probably will have to take the pin pro out