I agree with Array and yourself, I don't think I'd ever use it as a first name. I just don't love it enough to consider using it as a fn but I could use it as a middle name or nickname. I also have a friend named Alison who goes by Alix. When I first saw Alix' name written down, I thought it was a little strange. I'd just never heard of it before especially as a nn for Alison.
Miriam Alix is a terrific combo. I think that it flows very well. Miriam seems more traditional and sophisticated whereas Alix seems a little more modern (not necessarily trendy, though) and I really like the balance between the two.