These are actually logo'ed Quart, not MB Quart. Label on the cabinet likely says that too (or it may not). In the early 90's Quart became MB Quart adding the MB to call attention to their original mission, build instrument microphones. MB stood for mikrofon bau or microphone builder.
I worked at MB Quart when these were current and they represent pretty much every detail of the traditional German loudspeaker. Furniture grade, heavy veneer, staggering attention to detail, beautifully made driver components, and so on. The next generation that followed these was not as nicely made. I think these might even have glass tops too. Think Braun, Canton, and so on and you got these figured out.
Sound was pretty much traditional German 'Taunus Sound' as I recall in that they've got plenty of top but not too much bottom. No one was really won over by the MCS which was rightly called earlier a variovent and the technology was dropped. IIRC it was only used for 2 years tops. You may like them, you may not as far as how they sound. I liked the 2-way w/ 8" myself. So much cone area relative to the high frequency driver balanced out the sound decently.
And for $100, are you kidding me? If I hadn't so totally moved away from towers these would already be in my home, sound quality caveats or not.