I don't have a Mac, so this may not be much help, but looking at pages 8 and 9 of the manual and considering what you've said it sounds to me like it's offering a choice of location instead of installing by default into the Applications folder mentioned in the manual.
If that happened to me I'd probably create a folder off the C:\ drive and install to that.
I wonder if maybe it can't find the default folder so it's asking you what you want it to do?
Regarding the standalone version quitting unexpectedly, that's happened to me on the PC. It seized up a few times and then crashed out. I reinstalled and that seemed to solve the problem. It's running ok now, anyway.
Hopefully someone with Mac experience will be able to offer something more helpful, but as this forum is pretty quiet I thought I should try to help if possible.
I hope you manage to get it working soon. It's a great little program. I have a Mg Voyager and I still find the MiniMg V useful. And I was talking recently with a guy who recorded some classic MiniMg solos back in the 70s, and he spoke well of the Arturia.
