The key to owning a 217 is that you have the programming documented somewhere. If you have no real reason to upgrade, I would just grab another 217 for standby. The SX-200 is rock solid, and unless you see flames pouring out of the cabinet, some or all of it would be salvageable, even in a catastrophic failure.
That being said, the 200 wiring is not plug compatible with either the 50 or the ML/EL. A 200 spreads 6 8-port cards over 2 cables for 48 ports and they are in groups of 4. An ML/EL spreads 2 adjacent 12-port cards in a cable, but the 13th pair is the seperator. A 50 brings 16 ports out on each cable as the first 16 pairs.
You could create a hot standby with the switch you get so it would be numbered the same as your present switch, but it would be more sane to run new crosscuts. Especially since in a 200 the block probably reads 199,101,102,103,108,109,110,111 etc.
A MOSS sheet needs to be generated for the different changes to your ML/EL. I think the basic switch is 96 or 144 ports, so it doesn't apply in your case. Your BLUE card count is fixed on the MOSS sheet, and you can add WHITE cards up to the port allotment in the MOSS sheet.
Your card count would fit in a single shelf, 3 analog station cards, 1 digital, 1 or 2 trunks and an MEM if you're going the VM route. A MOSS sheet change requires a Mitel dealer or a good friend in the Mitel business.
And last, this is just a guess, but I think the ML looks like a huge file server, and the EL is a cardfile that mounts in a relay rack. I'm sure someone will enlighten us if that is wrong. Both support 96 ports in the first card file.
Of course, if you're looking for a new switch for corporate reasons, none of these switches would work, but that's another thread.
