Going through a search seems unnecessary if you have the release you want to add discs from open in the next tab. Ideally, we would be able to copy the URL, paste it in the "existing tracklist" field, and be given a list of its discs to choose which one to import.

Edit: Other option would be to take tracklist URLs - that would make implementation much simpler, but I guess tracklists are a bit too hidden right now for that to be good UX