I'm considering adding a couple of these to my Apollo 13 to go with my already-upgraded speakers...

http://www.parts-express.com/dayton-audio-dta-120-class-t-mini-amplifier-60-wpc--300-3800

Why? Because it just doesn't get very loud from the factory (my other games, WPC and Pin2k, positively destroy it volume-wise when they're being played at the same time), and on investigation the reason is quite clear -- the TDA2030s used and the supply voltage on said TDA amps (~13VDC regulated, and well-regulated in my example's case) only results in a roughly 8w output into 8 ohms.

8 watts isn't much, but a simple resistance bridge would drop that output down to line level quite easily and then feed a pair of Dayton's -- one for the backbox and one for the sub in the cabinet. The other possibility would be to design up a relatively small booster amp using a pair of the TDA2030s per channel; that would roughly triple the per-channel output, but likely would require separate power to be provided as well (as is the case for the Daytons, of course.)

Has anyone considered such an upgrade and/or done it on these Whitestar games? I guess I'm not really all that surprised at the (relatively) low output given the circuitry used to produce it... it's plenty clean and the stereo mix is nice, but the punch just isn't there.

A single amp is no good because there's actually three channels in the backbox; Apollo 13 is one of the few that actually has stereo sound plus the sub/low channel. With a better driver in the bottom cabinet (which I subbed in) it is quite impressive in that regard. I changed the speakers and the quality difference was immense -- now I'd just like some more juice

And yeah, the TDA is a good chip (I especially like its internal protection against destruction-by-short along with the excellent native noise floor), but I suspect the encoding leaves quite a bit to be desired. The easiest way to make it "plug and play" is to grab the signal at the existing output connector, use a resistor bridge to drop it to reasonable line level, and then feed the amp with that. This should also keep the noise floor down.

Except that it actually can't deliver the claimed wattage (look at the power supply; you can't cheat physics!)