Not quite straight forward. The upgrade to the 660 should not give any problems with the link to the Autocom, assuming it will be hard wired through the standard Autocom isolator, but you may have a problem with a Bluetooth phone.
I upgraded from a 2720 to a 550 with no problem. Then I changed bike so bought a new Autocom Logic with a new isolator for the 550 and linked my Palm via Bluetooth. Everything worked as it should.
Finally I changed to a 660 and had some problems due to the different "flavour" of Bluetooth on the 660. The Palm did not connect properly so I changed to a Blackberry. That was OK but making a call via the hard wired helmet headset resulted in me hearing the caller but they could not hear me.
Autocom told me they had found a problem with the 660 when used with their isolator and had developed a new one to fix the problem. They changed mine FOC and everything has worked since.