I just got my 2022 ST on Tuesday, and I'll be going to a local Car Audio store soon to get a quote on upgrading the stock system. I'll follow up with what they tell me regarding additional equipment needed (if any)!
So I got my new system, absolutely love it. Cost about $2K to upgrade all 6 speakers, then added a 10" sub in the back in a custom box that replaces the factory rear storage compartment cover. They put the amp in that storage compartment and I still have some usable space in there for any items I may want to keep in the vehicle, and can still move it to access the spare. This price included all install cost too, so doing it yourself can most likely be much cheaper, I just did not have the experience to do it properly myself. All in all, it sounds better than the B&O system that was in the vehicle I test drove and I am really happy with the result.
No specialty equipment needed, just speakers, sub, box, amp and wiring. The only thing you'll have to figure out is how you'd like to do your Sub.