Hello, i see you might not be working on this module anymore..
I've tried to use it, anyway, because i really needed a domain aware search functionality.
I must say it worked pretty well, i had some troubles getting the way to use search_api but then i saw the domain "data alteration", enabled it and the domain fields came up.
The index was created so i thought i would have worked but the search results were always the same, regardless of the domain being viewed.
I've spent some time trying to debug the query_alter hook, but i couldn't find a way to print the query since dpq() always gave me a white screen due to the excess of execution time.
This way i couldn't figure out what the problem was...
Thanks,
Da.