If you haven't already, you may want to pose this very question at the Apogee Acoustics User Group forum. There are some seriously knowledgeable and friendly Apogee users there that I'm sure could shed some light on this question.
FWIW, I've only listened to my Duetta Sigs with the MRT on the inside.
FWIW, I've only listened to my Duetta Sigs with the MRT on the inside.