You won’t need any additional driver, since, as you already said, it is already included in the kernel.
However, as owner of a RX6600, I can tell you that the GPU will be quite loud sometimes. I can recommend you to check out LACT, which let’s you define fan curves, which makes it A LOT less noisy.
I chose to continue with my current setup until I get the time and motivation to upgrade.
I will build a new server from scratch. For that, I bought an used mainboard for a few bucks, which has 6 SATA slots.