I'm with DonM regarding the PSR-740, though I'm biased as I own one. It's a powerful keyboard, particularly if you connect it to a computer with a good realtime sysex editor. Essentially you get an extended MU80 synth with built in keyboard. A friend has a PSR-630 and DGX300 which I play occasionally and it's a very frustrating experience playing the DGX after the 630 which is much better than the DGX and much nicer to play. With the DGX or 292 you're not going anywhere. Better to get something more advanced that you can grow into. And I would plump for Yamaha and a keyboard that has XG which gives you all that synth power.

Bryan