Sounds kinda like something that I did with my cab. It is a TMNT 4-player cab with a single/mono (JAMMA) speaker set in the center above the monitor. I wanted more for my MAME/DOSCab. Much, much more.
So, I hacked apart a cheap PC speaker set to get the amplifier and volume controls. I then added four 4" speakers into a new control panel box that I built. I took this path because I didn't want to clutter the space above the monitor with additional speakers. Two of the speakers are located on each side of the box (near the rear), while the other 2 are situated at the front panel's corners of the box. My box front has the front corners cut at a 15deg angle, onto which I installed the speakers. This adds some "width" to the sound. Then, I stuck a smallish subwoofer (6.5") into the corner of the cabinet interior for some bass. Finally, I wired the four new speakers, the sub, and the single JAMMA cab speaker via a passive surround wiring methodology that I found on the web:
http://allmanmusic.homestead.com/files/passive_surround_with_sub.gifLet me just say that this sounds GREAT! Compared to the old single speaker in the system, the multi-speaker sound is a no-brainer. When using the cabinet for MAME gaming, the sound seems to envelop the gamer with a holographic surround sound. Then, when listening to MP3s (via DOSCab), the sound fills the room with ease, with a wide and deep soundstage, even with a small amplifier. For a very small sum (about $25), I put the entire system together.
Oh, I almost forgot, instead of using traditional 4" speaker grilles to cover the control panel box's speakers, I decided to wrap the entire box with black speaker cloth. Radio Shack and other speaker parts retailers sell this stuff for about $15/roll. It looks great and keeps the sleek, black lines of the cabinet intact. I'm very pleased!!!