I started with Snapper purely because it's pretty quick to load, so no waiting around for 5 mins only to have something to go wrong at 4 1/2 mins in.

After some messing around with the original WAV file and the low pass filter on the PWM output i got the game to reliably load.  Once i'd figured out the correct process for producing the WAV files i tried a couple of other games which, after a little more filter tweaking, again loaded reliably.