Dan, don’t want to get too off track here but you mention the room itself, one other thing that was a game changer for me would be power related & specifically the outlet feeding your power distribution. Specifically the top of the line Furutech NCF outlet, had played with other outlets in the past with not much change, this one is a completely different animal. Now I’ve only used the North American version so not sure how the UK compares but if you’re interested at all, check out the Furutech Discussion thread, lots of info there.
Edit: Here’s a link to my first post talking about the outlet swap, if any interest: