The Triphonola is not an expression system akin to Aeolian's Themodist;
it is a full electrically-operated reproducing system.  There is a
picture of what the roll perforations look like on my web site under
"Music Rolls", on the second page of pictures there.  The URL is :-

  http://website.lineone.net/~agr/index2.html

I know very little about the way the system operates functionally
but will have a word with a few acquaintances who know more about them
about writing a bit for the MMD about it.  I believe the Musical Museum
at Brentford in London recently rebuilt their Triphonola grand --
another good reason to visit the wonderful museum!

Yours sincerely

Adam Ramet
agr@lineone.net