I have dozens of 6DJ8s to try in my RM-9 Mk I. While the NOS tubes do sound great the quietest tubes are my RAMs from Roger.
A note of caution, the tube sockets in this amp aren't made for constant tube rolling. They are merely soldered onto the board underneath. Pulling tubes out will eventually break the solder joint and you'll not be happy then! Find what sounds good quickly and stick with them. Roll to your heart's desire elsewhere in your system.