I used Firewire years ago, but after I upgraded my RME converter, it's now no longer an option. Steve Jobs said "Firewire is dead", in 2008, but in your particular case, I believe you should be fine for years to come. RME Driver support is as good as it gets long term, even for older comms technology and dis-continued RME gear.
If you happen to live near Perth, Western Australia, I could maybe, with your permission of course, test my newer RME gear on your system, which, if you yourself happen to upgrade in the future, would also be beneficial in giving you peace of mind. But myself, being located in one of the most isolated parts of the world, I'd hazard a guess the chances of living close by is nil. 😂
If someone else on the thread does live close by, with an up and running Proxmox Hackintosh, and wants to experiment with the audio capability, it will expand the knowledge base. Thus PM anytime. 😃
I guess if worse came to worse, maybe, I could install the same Startech Audio card as yourself, and find a firewire to thunderbolt adapter?
Firewire 800 should still be able to record about 55 channels of audio at 96khz which is still pretty good considering🤔
Prefer to use MADI though, as I can't daisy chain my 2 converters with thunderbolt/ firewire.😖