Mark - not familiar with the ps500 and it may well have better keybed. But at a glance it seems to me very limited as an arranger.
The P-S500 is the portable version of the CSP-150/170 modulo the usual Yamaha crazy. I play the CSP-170 and use the Smart Pianist app.
I usually call these a "digital piano with auto-accompaniment features." The CSPs, in particular, need the Smart Pianist app to access all of the internal features. The P-S500 provides some functionality through its front panel and needs Smart Pianist for full access. Smart Pianist supports adaptive styles a la DGX-670, but they need to be explicitly enabled. Smart Pianist displays four big buttons for changing MAIN sections and that means hitting the tablet screen while playing.
The biggest drawback is inability to add new styles or to do any sort of voice editing.
The P-S500 specs claim the same GHS keybed as DGX-670. I'll leave it to Mark to evaluate the feel as he gets to see and play everything.
The CSP-150/170 have better keybeds, but they're furniture. I like playing the CSP-170 NWX.
The biggest upside is additional high-quality piano voices -- Bösendorfer and C7 (AKA "Studio Grand") -- over the DGX-670. The P-S500 amplification/speaker system is different, too.
The P-S500 is going for $1,600 USD, so if someone wants upgraded piano vs. DGX-670, it's an option. Folks need to study the features carefully, tho', and decide if they can live with plain auto-accompaniment and Smart Pianist.
Smart Pianist is due for an update -- maybe when the CLP-800 series is announced?
We're getting pretty far from the original question...
-- pj