Yep a 28Mhz 030 will struggle to play this I'm afraid, esp. the GUI which is actually generated in 65,000 colors and converted to AGA 256 colors in real-time (ie it's slow).
If you look at the readme you can see there are options for enabling an audio requester at statup which will allow you to verify which AHI driver it's using. You should also try the audio playback rate right down to 8k.
I take it you are using v1.2.1?