Wow - that is awesome!
I tried the instructions in the thread and when I use
$If(<Disc Count>>1,$IsNull(<Set Subtitle>,"• Disc "<Disc#>" •","• Disc "<Disc#>" • "<Set Subtitle>" •"),$IsNull(<Set Subtitle>,,"• "<Set Subtitle>" •"))
as a virtual tag, MB complains that "The virtual tag could not be analyzed". I copied it from the forum post, so I'm pretty sure there is no typo.
Also - maybe I'm dumb, but I can't find a place to set this "Set Subtitle" tag.