Best speakers for my system

I'd say you need to go to lots of different dealers and listen to lots of different speakers. Your needs do not really rule much out (other than panel speakers due to the low ceiling), so you need to figure out what you like. Some stuff to listen to in addition to stuff already mentioned - Harbeth, Devore, Verity, Sonus Faber, Avalon, ProAc, B&W.

Take a listen to the ProAc "Response D38R"

Geoch and Countingbackwards, you both recommend Proac's, which are a speaker brand I have high regard for. I have not heard them with the Levinson gear of this genre (or with any Levinson amp for that matter). Have either of you? I would be interested in your opinions as to mating them with the ML amps.

My experience with the 331/2/3 .5 amps and the 334/5/6 amps is that they are a little bit more forgiving than say the Krell FPB/C amps, maybe slightly softer on the details or a bit less strident may be a better description. Almost a very slight "softer" (rolled off sounding top range) and slightly lighter in the bass, but not weak. I actually like both this line of Krell amps and also these ML amps - I am not picking one over the other. I am actually looking at a new (used) amp and the 334/5/6 or the FPB 300C or 350C amps are being considered (along with a Spectron Musician possibly).

I'm sorry, I haven't.
But this is my preference for a high current, high wattage, SS amp. I've heard them with Pass, Musical fidelity, Goldmund, Nagra, & over a dosen tube amps. & they can manage to keep their unique personality above any of them.
I've had the Response D28, D38, 5, 4 over the years & I think the newest D38R with the ribbon tweeter betters them all in compatibility as an all-rounder & value in this price category.
But I'm not shure about the matching with the ML once I've never heard them together.

Kind Regards

Given your equipment and room size, I would second the recommendation for the Thiel 3.7. They like tons of SS wattage, but after a long break-in period, they will really sing. They are at the top of your budget range, but I can't imagine that you would ever want for much more. I've been lucky to hear them twice and walked away both times extremely impressed, and with a severe case of speaker lust....