Sounds expensive! If you're looking to send hardwire IR to both, you'll probably need to send separate outputs from the connecting block to interface blocks for each - that is, unless both happen to use the same oddball signal

That's why I don't have either my 990 or my cable box on an interface module - both require the same one (as best as I can tell, details on the cable box are hard to come by) and I have no interest in buying two of them. If the 990's IR output jack (or the cable box's IR output jack) simply passed the incoming "interfaced" signal back out, though, you could potentially use one interface module for two devices. Just random scheming, though - probably won't ever do it.

I am using the Xantech 794-10 to feed the IR input to the 990, then, I noticed that the Sherwood and Pioneer IR settings for the 794-10 interface module are the same, so I connected the IR out of the 990 to the IN of my Pioneer Elite DV-79AVi and sure enough, now both units are controlled via the rear IR. Suffice it to say that the 990 IR output works, but only with compatible devices.

Also, I originally tried to use a regular IR target/receiver, by my LCD was interfering with it, so I am getting a LCD/CFL tolerant version to try and see if it solves my issue. The first lesson I learned in trouble shooting IR, turn off other "emmitters" when doing the initial install test.

Update to my last post, I got the Xantech LCD/CFL resistant dinky link and hooked up the interface module, success.

Two notes on the 794-10, I did have to ground the GND2 pin to the chassis, which I used the Phono ground for. Otherwise, the Pioneer would not work while the 990 would, but both work with the GND2 pin grounded to chassis. Lastly, the cables from the 794-10 output to the 990 IR Input and from the 990 IR output to the Pioneer IR Input are both 3.5mm stereo.

I am using an MX-800 and was of the understanding that I could take the output from my MRF-200 (that was formerly used for an Ir emitter) and plug it into the 990 Ir input. I expected that I might have to cut the output a little bit by using a series resistor. This is a surprise.

Exactly what does the 990 expect (voltage, current, data format) for an input? What kind of translation does an interface module perform? Is there an interface module for the MRF-200?

The 990's IR input will presumaly need an interface module to work with the typical IR output from something like your MRF-200. Outlaw identified the interface module for my Xantech equipment (the 794-10) for me; they may be able to help with yours as well.