I´ve got an Asus RX580 and a ESI Juli@ PCIe (thanks Raziel) in my X5000.
But remember that the X5000 Amiga OS4.1FE ISO installer don´t have support for RX cards, either use an older card during install and then install RX drivers or edit the ISO(search this forum) with RX drivers to install the OS directly with a RX card.
Also the NGFS(file system) on the X5000 ISO is outdated, Tony Wyatt the author of NGFS can help you out with a newer version.
People are being a bit misleading here on the sound card. Unless it has been re-released in the last week or so (I've been too busy to check in for a while) there is no driver available for it. There was but the author has withdrawn it. They intend to re-release it at some point but as far as I know that hasn't happened yet.
I fell into this trap too and bought an Audigy FX on peoples recommendations that is still sat in the box awaiting the driver re-release. I forget what I bought to replace it but it was only about £15 on Amazon. I have people round imminently but can look it up this evening if I remember.
Regarding the RX cards, did someone post instructions on how to install and what to edit in ISO for X5000? I searched through the forum and can only find forum threads for X1000. I was pretty sure this was covered at some point but I can't find it anywhere now. Thanks!