But for the scenario where a movement/act/piece is split-up over more than one track, that would probably mean transforming the field into an alphanumeric state.
That would also accommodate for what you regularly encounter with classical releases: having something like: II.a, II.b, II.c etc.
maybe to keep it numeric you could have 2.1, 2.2, 2.3 etc (being the equivalent of II.a, II.b, II.c etc) and do away with the hyphen (-) idea.
You could then have
track1 1.1/3 displayed as 1.a of 3
track2 1.2,2/3 displayed as 1.b/2 of 3
track3 3/3 displayed as 3 of 3