IR Input on Master

No chance directly connecting to an existing 2100/3100/4100 port for IR IN.

Current choices include a MET6N keypad (best price option for anything new from AMX). Our dealers use them in banks at the rack, fed by Xantech or other brand repeaters with concealed in-room pickups, or in some cases via a multi-control HDMI end-box-to-switcher repeater (Atlona and others).

You could slave a 700 or 900 just to get an input, but that's costly.

Obsolete choices include many things you can find on eBay, AXB-TCR, AXB-TM5, -TMC, -TM, plus wall units and the old tan swivel box units (which we have about 100 of, new in box, waiting maybe for you- email me).

IR Input on Master

Rather than IR, I use an AXR-RF to connect a MX900 to my AMX system. To save time and available channel numbers in the AMX program, I have it alongside a URC MRF base for IR control of some source devices. Just be sure to get the correct model -418 or -433 for the model URC or RTI you are using. This also eliminates the need to point the remote at a target or fuss with piggybacking a decent looking IR receiver onto the hideous AMX offerings.

Prior to this, I used a broken MET-6N as an IR receiver, which I probably still have laying around if you're interested.

Is this a Total Control system? If so, just use 232.

If this isn't a Total Control system, and you haven't yet sold the remotes, it would be a thing to consider. The remotes connect over Wi-Fi, so as long as the network is good you don't need to add and antennas or anything, just the URC processor that will talk to the AMX system.