I tried the plugin and it works great. Does exactly what I need it to do... Except for the fact that as soon as any other sound plays, you're right, it cuts off. Now I'm just using a text to speech wav file (created here
http://www2.research.att.com/~ttsweb/tts/demo.php) to play my emu announces, so they are fairly short. But I can see why you would have a bigger issue because some of yours are long, like the Neo Geo. These sounds are nice by the way, did you make them? What sounds are you using for your game launch and game end? The ones I'm using I'm not too thrilled about...
I think as far as addressing the sound cutoff issue we'd have to defer to Loadman since he's the man behind the plugin. I think, at least for that particular sound/event, it needs to run on it's own channel so it doesn't get clobbered. Possibly the only time it does get cut off is by another emu change event?