I owned both a S910 and a Tyros 4 at the same time. Had the opportunity for 6 months to compare them side by side, exchange setup between the two and generally do a very good comparison.

I played both keyboards through my Bose L1 Compacts and used very similar mixer setups and what I found was the S910 just could not match the Tyros 4 sound in any way. I eventually sold the S910 - kept the Tyros 4. I now have the S950 on order and will do the same side by side comparisons when it gets here on Tuesday. If it even comes close to the T4 sounds I will probably sell the Tyros 4 - if not the S950 will be sold. Time will tell.

Deane