Owning a Korg PA3X I really don't see why I need or want a second arranger. If I want extra sounds I use samples or VST's if I want styles from other brands I convert them or use Varranger.
I never understood people with 2 arrangers...
If you needed anything to a PA3X, it would be a Solosynth/Pro workstation/PC running VST, but not a 2nd arranger... because almost all styles can be converted and adjusted to your own arranger.
So a PC with VST's if you dont need any extra keys, and the others if you do need them... Personally i am a big fan of one instrument with weithed keys and another with unweighted synth action keys...