Trombone up to C6? You mean two octaves above middle C?

I hope they don't go that high!....and I'm a pro trombone player!

Two octaves above middle C is in the 'freak zone' of playing and no one would ever compose any 'playable' piece of music with that note in it. Maybe a special commission for a freaky player....but even then, it'd be a miracle if it got played correctly.

And in a sample  library? Why? That's trumpet range. Trombone samples sound like bad trumpets if transposed up that high.

Now....one octave above middle C is to be normally expected for any orchestral or any other music. Go on up to a D for sure. (ie: Brahms 2nd...brilliant writing for trombones!)

Anything above that is seldom written or played in orchestral literature, or requires an Alto trombone.

Excellent Jazz players will play up there usually without problem. (Bb, C, D, Eb, F)