One of the real drawbacks of Korg arrangers is the lack of any decent daw integration. I don't use half the buttons on my PA4X, and hardly ever touch the sliders either, and yet there is no way to assign any of them to midi CC. The PA5X is no better.
I enjoy my PA4X greatly, it's terrific for just getting an arrangement out quickly. But if you're also interested in DAW work then really you are going to need another keyboard.
Strangely, I use Korg's nanocontrol( for the sliders) and nanopad(for the transport controls). The nanopad site on the end of the PA4X looking untidy, but it does the job. I will often just record audio, rather than MIDI. I'll mix it on the PA4X using the sliders where needed, although it's usually balanced by the time I've finished with the songbook entry, and I use multiple takes for comping, to make up for my overambition at the keyboard. I often use mp3s I make in this way as backing tracks on the PA4X rather than styles, but that's a whole other story. I also have an AkaiMPK225 which I use as a midi keyboard and daw controller with my laptop on the kitchen table, when I want to be marginally less anti-social.
A long answer, but basically get a midi controller keyboard. The often have cheap ones on EBay, and the MPK49 comes up regularly.