Mike,
I should point out that I do not advocate Naim speakers as a panacea for all systemic ills, however I do feel that someone such as yourself who has garnered a certain level of expertise WRT a wide range of Naim's products should at least try Naim speakers in the context of your own system before suggesting that someone 'Ditch the SBLs'.
Having heard the same CDS2/52/500/NBL system as you, albeit in a different venue, I can't understand anyone suggesting that "there's something ultimately uninvolving".
Just as a point of reference as to where I am coming from, I will relate a short story...
At the Naim musical evening here in town last winter, Terry R brought along a live club recording of a little known, but superb, Blues band that coincidentally was booked into a club the following evening. At Terry's suggestion, I had the opportunity to listen to the entire CD at live volume levels on the Thursday evening, and subsequently listen to the band play live the following night. It was the first time in my life that I felt that a HiFi system truly came close to rivaling the real event. The sense of involvement experienced with the Naim system was not diminished by that experienced at the live performance.
That for me says more than any HiFi adjectives can.
I gather from your posts on this and the old forum that you have never heard any of the Naim loudspeakers in your own home (which I also understand has recently changed). They may indeed not be to your taste. My point is simply how do you know for sure?
The first time I heard IBLs at the dealers, I thought that they were somewhat anemic sounding. I now realise that I was hearing them at their worst as they were neither setup properly, nor were they broken in. My pair have seen many years of use and sound wonderful in my room on the end of a lowly Nait2 (please, no mullet comments as the pair cost me less than the Nait). They open a window onto the musical performance that is simply riveting. I have recently heard what a 250 can do for them and I can't even begin to describe how pleased I am with myself for earnestly tracking them down.
I should also point out that I have heard many of the Royd models and enjoy the Albions very much.
I am not suggesting the we all must like the same things. It is just that I don't believe that you have really heard anywhere near the potential of your current Naim gear.
Craig