...which is the weakest link in my audio chain?
For me (and probably many others) - it’s my ears. 😁
I second the notion of checking your room’s acoustics first, as your setup appears to be very capable. I had solved a confusing "smeariness" on the staging from my system that I attributed to the TVs screen being slightly skew to the listening position and not acoustically treated (I ended up throwing a blanket over it - helped immensely).
Bryston, from my experience, sometimes borders on the threadbare, but that Rega of yours should be able to fill out some of the thinness.
Yep - look at your room acoustics first.