i have also tried to do the multi reference as you have suggested. the issue here is i am unable to do anything with the product database so once i have created the multi reference in the collection i want to connect to, i am unable to add a new field for the the reference in the collection i want to connect from.
i cannot help to feel that i am back to stage one of my post re: complaining about the read only product database within the wix store app unable to add custom product information.