That's the 64 Million $ question, but reading through some of the product reviews for the HDMI Extender, it appears to work over Cat5e. There was a comment or two on issues with IR. I'm still trying to determine how they manage to send a maximum bitrate of 10.2 Gbps down Cat 5e which supports 1 Gb/s. The HDMI extender appears to support HDMI 1.3 based on the quoted data rate of 10.2 Gbps
Here's an interesting item that I came across: Most CableTV set-top boxes use HDMI 1.0 What you are going to have to determine is what version of HDMI the Nextbox is. It might be 1.0, but it might also be worth confirming it. That limits the data rate to 4.9 Gb/s.
Looking at the extender, there is no information as to whether or not the bitrate drops as you drop from 1080P to 720P for example. The question I have is what is the trade off between the Cat 5e cable length and the maximum bitrate that the cable will support before you start to see problems. I guess you will find out relatively soon. You might just become the forum expert on HDMI over ethernet
Generally.. there is nothing that should STOP it from working.
The nextbox.. really doesnt CARE what your connecting to it externally. I have one, that i regularily switch between a TV and then swtich cords over to a projector.. no issues, even while the box is on.
So in that aspect.. it should be FINE. Beyond that.. its how well the HDMI over ethernet works. We did use some of those, or similar (i think they were DVI over eithernet though.. but very much similar), at my previous job, and they seemed to do fine.
The biger part, will be looking more into... say by looking at the instructions for those devices on the manufacturers website, etc.. on how to set up the IR repeater portions, if you get one that has that.
From the looks of it... it likely will have a receiver at one end, over by where your TV will be. That receiver will have to sit somewhere where you point the remote to. It should then send that IR signal.. across the ethernet too, to the other end, where there will be a broadcaster module... this one will have to sit usually somewhere pointed INFRONT of the cable box, to send the signal out to change the channel, etc.
While its not the prettiest.. this is one reason i am GLAD the house i bought, had drop ceilings in the basement. Have been able to run an extra cable line across there... there is about... oh... 8 ethernet running up there, surround sound wires, etc.