For Audition CS6, I've reassigned zoom-in and -out to the keys "R" and "T" (like on Pro Tools). It does zoom. However, when holding down a key to zoom in or out (R or T), the key repeat function doesn't work. I don't think the key repeat function works at al within Audition CS6. Is this so?
My keyboard's keys DO repeat in all other programs though. I like to zoom in quickly to either the playhead or to the IN or OUT of a selection. Unfortunately, the end result is a mere one-zoom instance per one key click (down then up) instead of what our PC/Mac's keyboard's key repeat function could do (when using Pro Tools): allowing you to zoom in or out quickly by utilizing the computer system's keyboard key repeat function. As it is, I'm much slower having to "tap-tap-tap-tap-tap..." to zoom in and out. Intolerable!
The mouse scroll wheel DOES zoom in/out smoothly though, oddly enough.