Can I do this with sub-playlists now?

No.

Are you sure? What happens if you organise the mp3s into one playlist per quartet, then organise those playlists into a playlist called "Quartets" (or "Shostakovich"). Then set the Quartets playlist to be always-randomise (in Emplode's properties window).

Then, with shuffle turned off on the player, select the Quartets playlist. What you should get, is quartets in a random order, but with the movements in the right order within each one. If you don't, it's a bug!

Peter