re: min maj 6ths oK, this is what I am not getting, if I play C...

re: min maj 6ths oK, this is what I am not getting, if I play C on the piano, it will vibrate in hz at the rate to produce the note c, if I put my finger in the middle of the string, it would double the vibration thus making it a octave higher right?

The way I interperet your messege is that if I played C then A I would create a major 6th, but if I hit C, does that not hit the C string and cause that to vibrate and then if I hit A does that not vibrate a totally different string, but the hammer hits the string in a different position to make the major 6th? What does hitting C have to do with it?