Most people like their Mame cabs to play CD music (jukebox mode), DVD movies, etc. So full range with subwoofer is only way to go!
That's a rather bold statement. I think you'll find that the majority of people with cabs don't use it for multi-use. A lot of people do, but the majority don't.
I think my cab is one of the most multi-use I've seen on the forum, and I don't use it for playing CDs or movies. I might eventually set it up as an MP3 jukebox, but that's only because it happens to be using my best speakers at the moment. If it plays movies, it will be because it's the closest convenient DVD player to the television and has an s-video out - it doesn't have a built in monitor. (so far I've used it as a: beatmania box, video capture box (TiVO), classic systems emulator, Mame machine, file server, web server, all-purpose TV-output box)
Anyway, I think
all Mame games would sound perfect on a simple, cheap pair of speakers. Not even just classics. I don't remember any arcade games that used anything more than good speaker positioning to improve their sound. Reason is, the closer you are to a speaker, the better it sounds, even if it's low quality. (think about headphones

) You'll get good bass even from a generic 4" or 6" cone if you're close to it or it's mounted in a corner or the inside of a box you're standing close to. The only thing to avoid would be using a PC speaker set designed to have a sub, and not having the sub in it.
You might look for a cheap barebones amp at Radio Shack, and get a couple of cheap car audio speakers to mount in the wood itself, long as your video tube isn't close to where your speakers will be. You might get the whole system for $20 or $25 that way.