In InDesign CC, you can set your EPUB reader. In CS6, you cannot.
However, you can set the default EPUB reader in Mac OS X. In the Mac Finder, select a EPUB file, and choose File > Info. In the Open With section of the panel, choose Adobe Digital Editions. Click the Change All button to set that as the default applicaiton.
If you create an EPUB, you should test it against any available EPUB reader on any available platform as you don't know which one the user will have.
Follow Steve's advice.
Thank you! I will!
You'll likely see me around with plenty more questions coming!
Thanks so much!
Launching new career, so you'll see plenty of queries from me! So grateful for those who take the time to answer.