hi Chris,
ah.. just checked -I wasn't aware that Yamaha still offers some packs in ppf format. And about converting custom voices, you're absolutely right (again).
I don't have this pack installed on keyboard right now, but I can see that there's only one voice and two Cuban percussion kits. Voice is not used in any style (is there only for MultiPads I guess), and Cuban kits are only used in three styles.
In few styles PSR-SX specific voices are used for Intros & Endings, but main variations of all styles should play just fine on PSR-S950 I think.
Bogdan