Are you certain the *.SND files you have obtained from the net are from an MPC
Or are they the Motorola *.SND / *.AU format ....
This other type of *.SND is often confused as an MPC type of file when in fact it's VERY different.
Try out AWAVE STUDIO.
It will tell you what the input sounds are for certain.
Run it in batch mode and convert many files at once from just about any format to nearly every other format. ( batch may be restricted in demo mode but you can at least try them one at a time per session )
A worthy addition to the toolkit.
With this and one of the other MPC editing tools you won't be beat ....
Rohan.