Personally i dont see the need for more then a single arranger in your setup...

Adding a synth workstation or stage piano to your arranger adds much much more then a 2nd high end arranger... My Kronos 88 Adds a lot to my Tyros5 ... ( stagepiano, synths, karma, high end drums, near limitless expandabillity)

Also think that yamaha montage8 combined with the pa4x also makes a comparable combination..... Or pa4x plus Jupiter80 or RD800 if you dont like the typicall yamaha sound.

But having 2 arrangers in a single setup, what would that bring you?