Can I use an ATI FirePro v4800 running in my computer and want to add an RX580 for power.
Is it possible to run them both and use the FirePro for 10 bit output while using the RX580 for processing power in Photoshop etc.?
No. You have to decide which card you will be using at most and install the driver for that specific card. The other card needs to run with Microsoft generic driver.