Hi Stephen,
You would certainly enjoy having the portable Roland RD-88 weighted action digital piano as a worthy addition to your collection of top-of –the-line Arrangers.
Since you already own the GENOS and the PSR-SX900 along with the Yamaha CVP-307 Clavinova and Korg Pa4X it may be superfluous to add the DGX670.
You could use the RD-88 as a portable controller for the GENOS or the PRS-SX900 or the Pa4X.
The Yamaha DGX670 will be too bulky and heavy weighing in at 47 lbs.
David, Thanks for even more useful information. I think you said it best ,having the DGX670 would be superfluous.