OK, here’s where I am with this at the moment and I’m very happy with the way it's going but if anyone wants to suggest any tweaks or improvements, I’d be very keen to hear them.
It’s clear that the “Sort by” function simply doesn’t work in MC for many fields, including Disc #. So if you have a box set of, say, 50 classical CDs and you want to display them in the same order as they appear in the box, you have to find a workaround.
The one I’m using is based on the very helpful suggestions put forward by tiberiuspv and MikeO. Here’s an attempt at a beginner’s guide.
1. Tag all the discs in each set with: a) the disc number in the Disc # field and b) the name of the box set, using the Series field.
2. Set up a view scheme in the tree called (for example) Classical Collections. Right click on Customise view and set rules as follows:
View As: Categories.
Show Categories in This Order:
Series
Expression
For Expression, click on Edit and enter the following Expression: [Disc #] [Album]
Click on Set rules for file display. The rule is: “Series” “is” and then choose the names of all the box sets that you want to appear in this view scheme.
4. With any luck, you'll end up with something like this:
The only thing that looks slightly odd is that when you mouse over the collections, the words “Play expression file” appear above the name of the collection instead of “Play albums”.
But the stack looks lovely when you open it. Look:
Again, the only slightly weird thing is that tab at the top, which says Mercury Box 1 Expression instead of Mercury Box 1 albums.
Coupla points:
1. You’re probably thinking, “Wouldn’t it be a lot easier to just stick the disc number in front of the album title? Then the discs would sort themselves into the correct order and all of this would be unnecessary.” That’s true. The only problem is that those numbers can look ugly when they appear as part of the album title in other views. Using the technique above, you never see the disc number in any view except the specific view I’ve pictured above.
2. These views display beautifully in JRemote, with none of those references to “Expressions” or other oddities.
3. MikeO, as you may have spotted, I haven’t used exactly the Expression wording you suggested and I may not have done what you intended so please correct me if I’ve done something wrong.