I have owned Tyros 2, PSR S910 and Tyros 4 in the past.

The PSR S910 has every sound from the Tyros 2 plus ALL the new Synth sounds and Pads from the Tyros 3. It also has the middle eastern drum kits which were on the T3.

- It has better Mega guitar voicing.
- MP3 and Audio player
- MP3 recorder

The Tyros line has a FAR BETTER keybed with after touch AND can layer 3 voices in the right hand(Upper 1, 2 and 3).

The PSR S950 obviously includes all the same sounds as the S910 but in additional a few other upgrades such as:

- Better concert grand piano sound from the Tyros 3 (which is almost the exact same as the SA Concert Grand on the Tyros 4)

- new standard and rock drum kits from Tyros 4 which will freshen things up over the tyros 2 and S910.

- Additional SA voices taken randomly from T3 and maybe T4.

- Its black and much smaller and lighter than the Tyros line

...but the biggest drawback seems to be that it still doesn't have any SA 2 voices or any of the choir voices from the Tyros 4... plus... dont forget those rubber buttons!!

good luck,
Nick