That explains some... You'll have to create a "Sounds" folder inside the AcesHigh folder. IIRC check6 is the name for the file, I might be wrong, though, it's been ages since I've used other than the default sounds. Anyway, the default is included inside the code and that is why you can't see the original...
Another way to find out would be to download any of the sound packs and see the specs from there. You don't even have to install the whole pack if you don't want to. You can choose one or more sounds, anything that's not represented in the "Sounds" folder will continue working as default. For your personal use it's even alright to mix the sounds of different packs. Just a reminder: The packs are more or less copyrighted material, so you can't publish the mix you might compile without permission of all who have been creating the sounds.