I am the same as you with this, too many things missing from the SX900, but along with what you said above, one of the other main reasons for me was the scat voices, that was a complete must otherwise it would have been the same as using my S975 but the inclusion of them in the SX900 brings it in line with at least the T4 onwards which was something I was always after.

That said, I think the SX700 is around a grand cheaper than the SX900 in some places in the UK at least, and that's quite a huge saving if the extras didn't matter much.

The SX900 is slowly becoming probably the best keyboard I've ever owned, it's that good.