Sorry to those who are awake - I'm ill in bed :-(
It is 256 steps, not 64.
So a given 24 bit signal has 65,536 x (2 to the power of 8) more - steps than a 16 bit signal.
Which, if my brain is finally in gear ( through the haze of prescription drugs - "much cheaper than your local dealer" according to Mr Mark Thomas ), - is 33,554,432 steps - just a "tad" more accurate, than 16 bit.
does that clarify ?