JD, there are lots of options at your disposal, and as stated above and on the PSR Tutorial, the multi-pads are liked to the OTS and stored within the style file itself.

Option #1 - You can create your own custom style with your own OTS and multi-pads right on the keyboard, and using the onboard style. It's very easy to do.

Option #2 - Use a registration to select the items you wish, including your own, custom voices.

Option #3 - Store your custom voices in the User Voice area, where they can be quickly and easily accessed.

There are probably more options available, but these immediately came to mind.

Good luck,

Gary