My preference is for natural sound as well. Pass Labs X250.5 that I own for 2 years now fits the bill. I listen to a wide range of music, anything from Metallica to Mahler. The Pass has no problems driving my B&Ws, although they're more efficient than the MBLs. I doubt Pass would have any issues driving the MBLs. I looked at your system and you have very nice components. Another thing with Pass amp is that it is very transparent and lets you hear what each component before it is doing. I recently tried 3 preamplifiers in my system, and each time Pass revealed their strengths and weaknesses. It's a great amp.
Good luck with your search.
Good luck with your search.