I think he's referring to the CNIRGW IR receiver, which allows the Crestron controller to respond to IR signals. The CNXLIR is used to learn IR codes for controlling equipment.

The CNIRGW *is* expensive, but it's very reliable and provides quick response. Another advantage is that it connects to the Cresnet bus, and doesn't require a serial port (or the additional associated programming).

As an alternative, I've used the Adicon Ocelot, and I've heard of others using Xantech's IRS232 or a unit made by Celadon, with good results. Here are some previous posts regarding IR to serial converters:

[Link: remotecentral.com]
[Link: remotecentral.com]
[Link: remotecentral.com]
[Link: remotecentral.com]

The Slink-e should also work, but I've never heard of anyone using it with Crestron in that way.