9201 I have a few 720,s that are used with some TIE trunks, some are 61's back to an 81 with 720's on one end or both.(all rls 4.5) and also a couple of 11c's that come back to the 81 to a 720. These all have "D" channels.
I seem to recall something about issues with clocking and FNF networks.
sporty2