I would never use any kind of pressed board for a player system.
I realize Universal Piano did but they covered the boards with contact
paper.  I don't trust this substance.  It is not solid and non-solid
wood is always a source of leakage.  It also responds to moisture by
swelling and falling apart.

When replacing any part in a player system bellows, I prefer to use
Baltic or Finnish birch plywood which is very high quality, with few
knots and very thin layers inside.  The major pipe organ builders use
this exclusively and it is _way_ more dependably airtight than anything
else out there.  I still shellac it but I feel you could use it without
the shellac.

Doug L. Bullock
http://thepianoworld.com/