I've heard both of the products you mentioned, one in the context of another system which had other MBL products and thought it was superb and the other one in the context of my own system which I now own. (The 8th wonder
) Both are superb in my opinion but system synergy is very important and I found the Ayre KX-R a perfect match for mine. It would have been interesting to also audition the MBL preamp in my own system but due to the complex nature of a trade with my local dealer that was not feasable and the Ayre KX-R reigns supreme in my system.
The feedback of other owners and those that have auditioned the KX-R has been very positive as well.