If I may intercede, I would like to offer a slightly different opinion.
It is perfectly fine to enter either the “performer” or the “composer” into the Album Artist tag. Of course the performers should also be in the performer and the composer in the composer tag, but you can chose either as the “Album Artist” tag in classical music albums. As long as the tags are consistent, it does not confuse ROON at all. (There is a lengthy, but in between quite interesting thread here, where this subject was discussed – among other things – at length, so I don’t need to reiterate it all her: Roon splits up tracks from some albums. Why? ).
But to sum it up: I have a decently sized collection of lossless high-res albums, thousands of albums, many classical albums, and almost all of them (or at least the vast majority) have the composer as “Album Artist”. I want my Beethoven sonatas under the “Ludwig van Beethoven” folder, and not spread out among Brendel, Levit, Barenboim etc. So the “Album Artist” tag is the unifying element, and I would find it very hard to keep my collection at bay or decently sorted if the classical albums were suddenly spread out in performer rather than composer folders.
Now it’s true that in the artist tag there should be the “artist”, so it’s easy to identify which recording it is, but I assure you ROON has no issues recognizing classical music albums when the composer is in the album artist tag
I have thousands of classical music albums where the composer is the “Album Artist”. Not once was there an issue because of that.
What is true, however, and that is the important thing: like Mike said, the “Album Artist” tag is what holds the album together, it is what unifies the album. So ONE “Album Artist” per album obviously. So that may be “Hélène Grimaud” on an album with composers such as John Corigliano, Ludwig van Beethoven and Arvo Pärt, but it can also be “George Gershwin” on an album with performers such as Leonard Bernstein and Gil Shaham.
For ROON, the important issue is not whether “album artist” is the performer or the composer, but that it is a unifying tag.