Here's a bit more from the email:

". Both PSR-S750 and PSR-S950 feature a larger speaker box for a full, powerful sound with deep lows and clear highs, highly efficient amplifiers with significantly reduced energy consumption and Flash ROM that expands the Voices and Styles ⎯ including Audio Styles on PSR-S950 ⎯ from Yamaha's ever-growing library. Both are pro-class digital music workstations with stellar sounds and mixing capabilities."