Optimized for use with Avidyne Integrated Flight Displays (IFDs), the AMX240 enables Com Frequency decoding and Frequency Monitoring of the two transmit and four receive channels of the IFD’s Com audio. ...  When interfaced with the AMX240, the IFD540, the IFD440 and the IFD5000 (Release 9) are able to decode the active Com frequency and display the agency name. At a glance, you know with whom you will be talking when you key your mic.

I can understand the AMX240 being required for the "monitor standby freqs" function.  However, I do not understand the IFD's dependency on the AMX240 for the Com/Nav freq decoding feature.  The IFD540 Pilot's Manual does not say anything about requiring an AMX240 for that feature (see "Cool Feature" box on p. 1-17 of Pilot Guide, here:   http://www.avidyne.com/publications/ifd540/600-00300-000.pdf" rel="nofollow - http://www.avidyne.com/publications/ifd540/600-00300-000.pdf ):

Decoded Agency Identifier The agency (e.g. Clearance Delivery, Ground, Tower, Approach, etc) for the Active and each displayed Standby com frequency are displayed in each com frequency slot. This is a handy reminder of the agency to which you have tuned in each slot. Similarly, if the frequency displayed is a nav frequency, then the Morse code decoded identifier will be displayed and will stay displayed for as long as the IFD can decode the Morse code, which serves as a usable means to Tune-Identify-Monitor.

Did someone in the marketing department get a little overzealous with the AMX240's role in com freq decoding on the IFD's, or what?

But, you are right, there is no need for the AMX240 to be present to get this function on the IFD540.  We always decode the agency identifier for all active and standby frequencies that are displayed on the IFD540, no matter what the audio panel may be.

Does MON1 work even if you've got both COM1 & 2 selected and active?  Just want to confirm my assumption that monitoring ATIS on MON1 does not come at the expense of audio from a Garmin COM2.