I use Custom Web Link searches within MusicBee's Now Playing and Track Information interfaces a LOT, and recently was able to spec out a link that works for specifying elements within Discog's "Advanced Search" (https://www.discogs.com/search/advanced) template. I originally posted this as a reply within a user thread of the "Wishlist" forum but thought I'd put it here in case it can help others as well. The following string put in the MB Preferences/Internet/Custom Web Links window will provide a way to specify one or more tag fields to perform an advanced Discogs search using its own field algorithms; in this example, <Artist> and <Year> are the desired search criteria:
https://www.discogs.com/search/?type=all&title=&artist=<Artist>&label=&track=&catno=&barcode=&anv=&format=&credit=&genre=&style=&country=&year=<Year>&submitter=&contributor=&matrix=&advanced=1
From my experimenting, attempting to truncate out all the empty, non-used fields like "submitter", etc. can produce bad results. Following the above example, you can add other tag elements (or remove the <Artist> and/or <Year> I have used) to get the type of search you are interested in. I had previously used a simple search link for a desired field like ".../search?&q=<Artist>" for example, but that performs a "keyword" search on Discogs from the Artist tag and can produce a lot of irrelevant results.