With the Ref2 MkII you can tube roll the rectifier (5AR4) and power regulator (6L6GC) tube. I haven't tried swapping tubes on my unit yet as the stock tubes sound quite good.
I also don't find the Ref2 MkII "bright" per se but it is quite precise and 'neutral'. It seems to get out of the way of the signal and yet imparts a pleasing flow and musicality. I've heard the LS2B and LS5 MkII; these older units do exhibit more traditional tube bloom and warmth.
Thanks for the great responses. I have a Ref 2 mk1 on it's way. If it's a keeper, I'll have to let go of my LS25 mk2 and my LS16 mk1. I hope the Ref 2 mk1 gives me the dynamics, detail and resolution of the LS 25 mk2 and the bloom of the LS16 mk1.
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