I have Audition CS6 and want to record an insert without overwriting the recording (just push the existing audio down the timeline). Any help would be great!
Audition doesn't work like that, I'm afraid - it preserves your files!
What you have to do is to record your insert separately, and then, in Multitrack view, find the point where you want to insert your new audio, get the playhead there and right-click. You'll get an option to 'split' the file - this will appear to make it like two files. You can now move the section on the right along a bit, and insert your new clip in the gap. You get the option to trim the in and out points (you can drag the actual end of the first section backwards and forwards until it's exactly correct0, and you can overlap the join with your new file so they crossfade if you want. It's generally better to do this, even if it's a very short overlap, because it reduces the chances of clicks occuring very considerably. Then you get the part of the file that you split off and drag it back to the end of your insert (same thing as you did the other end). Mix down the result, save the new file, and you're done.
What's actually happening is that you haven't destroyed any files at all - this whole process takes place non-destructively. You can't do this in Waveform view though - that's destructive and it won't give you any option to move things around. You could do it if you were desperate, but you'd have to use a clipboard and open-append. It's a lot less flexible, and you don't get the manipulation options you get in Multitrack mode.