Audio Research IR input

Nothing specific needed, just plug the mini-plug into the IR input. Something like this should work fine:
https://www.amazon.com/dp/B002JSDHCY/ref=psdc_3236443011_t1_B01LXO79CL

There are more expensive alternatives from Crutchfield, though I'm not sure why they are so much more.

In my experience with remote IR sensors the problem 9 times out of 10 is that the re-emitter is too close and is overloading the sensor. This is especially common if you are installing the amp in a cabinet say and don't have much room to operate

The sensors in ARC kit are pretty sensitive, for example they work well when I used to bounce my IR signal to my Ref 40 off my speakers! 

Does the extension work with the cabinet doors open and the re-emitter 3' or more from the amp? If not then there may be a problem with the re-emitter, can you test it on another component?

If it works have you tried mounting the emitter on top of the amp and in effect bouncing the signal off the inside of the cabinet? This often works well I've found

Anyway knowing more about how you have the system configured could be helpful.

If using extention cable for IR, plugs must also have mini mono end.

I'm doubtful about the necessity of a mono mini plug.  A "stereo" mini works fine for the 12V trigger so should work fine for IR. 

Thanks for all the responses. That is the sensor I tried. I also tried the 38 hz version. Talked to Audio Research this am. They were helpful and I will post what works shortly.

Well, have tried all the above on a ref 6 and ref 3 phono with no success. There must be another way to activate the sensor. Need to get back with Audio Research after the holiday.