I haven't tried the Bryston XLR's but I've been fortunate enough recently to borrow from Chord their Anthem 2 and Sarum XLR's + their Signature and Sarum speaker cable, the retail price on the Sarum setup is £7600, crazy money.
I've been living with them for a week and going from Atlas RCA's I was amazed at the extra detail either of the different XLR's gave me, there was also better separation with instruments and the soundstage grew in width and height, but after a week they just weren't for me. For all the great things they did to my system the vocals just sounded to0 empty and neutral, for some reason they had lost the little bit of warmth, richness and weight I like.
I'm convinced though with my little test that Bryston works really well with XLR, better that RCA, I just need to find a XLR cable that I like.