I just can't find a program similar to Cool Edit Pro for the Mac. Any idea?
Cool Edit Pro is now Adobe Audition. They have started a beta, so you're in luck.
Both can use your existing sound interface. If you want an easier (in my opinion) user interface, check into ProTools, but you will need to buy compatible hardware.
As a fellow Cool Edit user, I recently started doing some basic single track recording on Mac. The best app I've come across so far has been Sound Studio by Felt Tip Inc http://felttip.com/ss/ (You'll need the older version created by FreeVerse for older versions of OSX). I'm planning to experiment with some other apps listed here: http://www.pure-mac.com/audio.html but will most likely purchase Felt Tip, as so far, it has served me well.