BAT VK50SE or CJ Premier 16LS Series ll

I would like to know if there is a change of impedance mis-match? Can anyone explain this to me? I've been hearing alot of it lately

From my opinion, this is going to be great sell both of your amps don't run rotel with a fine Nautilus 802. Sell them both buying a ML 335 and CJ16LS or 17LS you will be set for awhile you will have both HI-FI sound a Musical sweet music , CJ will put out that analytical sound from ML and give you that sweet vocal and outstanding midrange.
You probably wondering why I did not mention anything about the bottom end because I know ML will drive that nautilus of your without any problem neither with CJ or BAT.

The "impedance mismatch" you refer to has to do with the ratio of the preamp's output impedance to an amp's input impedance. Basically, the higher the preamp's output impedance is, the higher the amp's input impedance should be. The C-J's design means it will have a somewhat higher output impedance than a lot of other pre's, so don't pair it with an amplifier that has an especially low input impedance. I believe that anything upwards of about 20k ohm for the amp will be OK, and this means most amps will work alright (50 - 100k ohm is typical for many amps). The other possible effects that a highish preamp output impedance could produce are capacitve high-frequency losses if very long cable runs to the amps are required, and there also may be some issues involved with splitting the outputs to feed multiple amps when biamping. I wouldn't hesitate to contact C-J with any questions related to your choice, even if only to double-check what your dealer may tell you.

I would save a bunch of dough and buy 2 Cary Rocket 88s and the Cary 2002 preamp and vertically biamp. You can even try it with one, or get a single V12. Once you go tubes, you will forget Rotel and JDRG (which I have owned both btw).

Dennis Had has done this with 801s and was one of the best sound rooms at CES. Can't wait to hear this combo at HE2002.

Since you are considering BAT, I can tell you that a vk500 and the 50se pre will give you power, dynamics, and a very well rounded but not overly beautified sound. My 2 cents are based on my experience with a 50se, vk1000's, and 801's.
Have fun!