I currently have CEP 2.1, Adobe Audition 1.5 and 2.0 on my computer. No problems...since each one was an upgrade, I had to install from the beginning.
I think I have settled on 1.5 to use. It's compatible with
my Mackie Control Universal and I've gotten too old and set in my ways to learn new procedures for mixdowns.
Another issue is that 2.0 saves EVERYTHING. Someone posted a utility here to reduce the size of the files, but you have to launch the utility every time you want to save a file without all the alternate takes, punch-ins and whatnot. You can tell 2.0 NOT to save it all, but that didn't occur to me until I had 20 songs that took up 33 GB!
AA 2.0 also makes you name and save your new session before you start recording, which annoyed me, even though I learned about saving the hard way.
Other issues that may be important is that 2.0 use VST (1.5 required a wrapper) and is ASIO enabled. For me, the native sound drivers have always worked fine for multi-track inputs, so that's not important.
However, 2.0 uses a very different way of configuring I/Os: in 1.5, you go to Options/Devices and set them there. With 2.0, you set them and then go to Edit/Save as Default Session or you'll find yourself setting it up all over again each time you open it up.
Since my boot drive developed the bad habit of requiring me to reinstall ASIO each time I started it up, that seemed to be a lot of trouble.
The differences in workflow are what really drove me back to 1.5...but I still have 2.0, and it may yet get used, especially if I record a guitarist with beau coups of finger squeaks: 2.0 has the only tool for getting rid of those that I've found.
Right now I'm editing a bunch of songs that were recorded to 8-track digital (Krog D888) at rehearsal; it's very easy to dump each one into 1.5 and deal with it there (each "song" is up to an hour long and contains maybe 10 individual tunes). Since I have 35 or so of the individual tunes, I wanted to use a program where I wasn't constantly trying to remember where it did what! Since I've been using CEP/AA since 05/2000 (CEP 1.2a) I went with the familiar.