the extra key would technically be called a 'G# trill key', and it really is useless, thats why no one puts them on horns anymore for the neck, you should be able to just throw the mpc on all the way, and then adjust intonation by turning the microtuner on the neck

I need to get a new mpc for my 6m so I can start having fun with it... anyway, yes it has a G# trill key and it's pretty useless unless you're doing a trill. My 10M tenor has that and a Eb one that's currently not active. The microtuner is easy... righty-tighty and it goes in, lefty-loosey and it comes out! =)

I played a 6m for 8 years. Great horn. G# is usefull because of the sax design. People that say it's not makes me question if they really have a 6m. Not really, but I still ponder their answer. The 6M is designed witth bell keys on the backside, to allow for the bell artwork. I am sure there is other reason, just this is the most obvious. Because of this the Spatula keys go in the oposite direction then most horns. Because of this, the normal G# trill would be the most aukward thing in the world to try to trill with. That's why they have the G# trill, to be able to smothly trill G#. If you can smothly trill with the normal G# you have just recently been descovered to have the strongest pinky on the earth and the Giness Book officials will be right over. The Micro tuner? Well the short answer, don't use it even if it works. Mine worked great, I still didn't use it. Why? Because on the inside of the chamber as you extend the neck it exposes the rivits to the air flow causing unwanted air direction changes. Now I have to say I was only told this, I have never taken it apart to verify it. But for me the explaination seemed right, as I can't think of a way if the next extened it wouldn't change the air flow. Hope that helped, enjoy the horn I allways did.