I would also recommend using OCLP: What is OpenCore? | OpenCore Legacy Patcher on your vintage MacPro.
I’m running a 2009 MacPro, firmware hacked to be a 2010 MacPro (they both have the same backplane). I have a Metal capable video card and I used OCLP to upgrade my MacPro to MacOS BigSur from Mojave.
I’ve been running Roon 2.0 without issue and considering the age of my MacPro it runs extremely stable, although it isn’t pushed too hard anymore.
I’ve done many upgrades to over the years. It started out life with dual 2.26GHz processors I upgraded to dual 3.06 GHz. Ram is at 24GB. I have three SSD drives in the bays and one 6TB hard drive, a 3TB drive for backups in the CD bay, below the CD drive.
I’ve upgraded the Wi-Fi and Bluetooth card and fitted an external antenna for the Bluetooth on the rear of the case.
My OS is on a Samsung 980 Pro NVMe in a PCIe slot.
It all sings along (touch wood) quite merrily.
If you do go down this route you will need to make sure that your Bluetooth/wifi card is compatible as well, although there are patches to help with this.
It took a while to work out but it was worth it.
Mr.Macintosh https://www.youtube.com/c/MrMacintoshBlog has some excellent tutorials to get you going and there is plenty of help on the MacRumors forum.