For my own notes and to help others, I have created the following wiki page that documents the steps I use to create AVD images by hand from the Terminal prompt, using Visual Studio for the Mac.
I hope you find it useful. Since the "Google Emulator Manager" GUI is not available on the Alpha channel (it's being rewritten, according to the dialog), I found these steps necessary to create an API Level 25 Android image for testing. The process was not without challenges but hopefully the above write-up will make it painless.
Since the above link is to a wiki, it is possible to create an account and edit the document as needed.