Since we recently had the topic of migration again, I thought I dig up this very old post.
Once a post has gotten an answer it is probably best to not migrate it; especially when it is on topic here. There is still the possibility to do it, but I think there is a superior way to take. First of all you may want to check the target site, maybe in chat and ask if such a question would be on topic and if you would receive a vastly different answer.
You are right, that cross-posting (not only within the network) is discouraged, but there may be some exceptions. In principle the same guidelines apply as if you were asking on the same site. Just treat it as a follow-up question. That means, ask your question again, but this time include what you have already learned, and link back to the original. If you want to have another point of view, you should already include which point of view you have gotten.
There is also nothing wrong asking about the same topic on different sites if you want to shift the focus of your question, for example: You might ask "What shape of apple is ideal for throwing?" on physics.se, and here you might ask "What chemical composition is ideal for creating the best apple to throw?", and on philosophy.se you ask "Is an apple optimised for throwing a scientific accomplishment?"*
* I have no idea about philosophy.