5 years ago in George Kayes store he sung the praises of Yamahas 900 (I believe), but said the sequencer for Korgs PA4X at the time was far superior.

I went Korg as I need to replace parts which at the time George said you could not, or maybe not well ???

After watching videos today it seems you can now record and replace drums AFTER you have sequenced, and maybe some of the other 6?...As well as 8 other tracks for sure..

Thinking of this as a songwriting partner, but I need flexibility...

I want to get another PA 4X but financing would be $1450 down....To get the PSR-SX900 is about $200 down...

You're comparing apples and oranges... Of course the PA4X is more expensive. Korg's PA1000 is most comparable to the PSR-SX900.

IMO sequencing on the Korg- all facets of it- is still FAR more capable than what Yamaha offers. Korgs have a true Backing Sequence mode, where you can do a quick record using a style, and then edit the recorded chords, "control track," etc., and re-expand into a full MIDI. I'm pretty sure Yamahas still don't offer this. Yamaha's implementation of step recording, and the "CHD" tab in its Song Creator has much potential, but since 2001 was never fully implemented IMO. Even some recent Casios are better!

Yamaha won't even let you view, edit, or tweak track events in the factory styles. [You might be able to download them off the board, "crack" the protected style with a 3rd-party utility on the PC, and then edit. But not on the board itself.]

The PA1000 also has a chord sequencer, which can be used in real-time, or you can store your favorite chord progressions as a sequence and use them to drive the arranger for a song, or just to audition various styles. I think the Genos might have a chord sequencer, not sure about the PSR-SX900. Personally I would choose either of the Korgs over the PSR.

Much as I love my Tyros 3, and before that the PSR3000, I do almost all my sequence editing on a PC other than transposition (the keyboards understand megavoices better) and occasional revoice and level adjustments.

I'm thinking about getting an SX900 and whilst I believe that the sequencer has been improved it would need to be a pretty radical update to make a difference to my workflow, and I don't think this is the case.

Korg sequencer still way better for editing.

The SX (and (after a recent update the Genos) has a Chord Looper which is a type of chord sequencer.