Don't know how much you would have to spend to upgrade from Tyros 2 to PSR950 but personally I would never consider such a move. Probably for slightly more money you can get yourself the brand new KORG PA600 in addition to your Tyros 2 and have the best (...well nearly the best) of both worlds !!!!!!

regards,
John

P.S. I have the PSR-S900 in combination with the PA800 and am truly pleased with my set up. Sure, if I were a professional entertainer or had buckets full of money I would probably go for the PA3X and Tyros 4, or rather the PSR910 as it is less bulky. Nonetheless in view of your question and ( I presume) budget I think it worthwile considering what I remarked above.....