Tom and I have just been trying an FSX Multiplay session. Works OK apart from its inflexibillity, once the Host is set up. From then on it's not possible to change aircraft, slew, etc etc. Although we opted to share cockpits we couldn't see a way of controlling the other aircraft.
I've got my router sorted and set up an FSHost session, just to check that I could. It appears in FSHostSpy and the session name is RAMSEY. Password is FAIRWAY. I've left a Tobago GT21 parked at Haverfordwest, in case anyone wishes to check that they can get in. I'll leave it running, though I've benn called (summoned!) away.
In the FSX MP session we used the PCI Voice Client on JHB_OPS and that worked as normal.