At the risk of throwing you off your plan, may I suggest an alternative to the IR blaster setup you are proposing to use? Not that the Sewell system would not work for you (it appears to be well reviewed by those who use it), but I had a similar problem as you (TV above fireplace, components in media closet in another room) and I found an all in one solution that works extremely well.
I opted to upgrade from a NextGen remote extender and recently installed a "Harmony Smart Control" system.
I ran a 50' 3.5mm audio patch cable through the junction box behind the TV, using an existing fish line that I left in the wall from the last cable run. You could do something similar and save your RJ45 to hardwire your TV for internet (instead of relying on wifi)
Here's my setup:
Items in top red circle have all been replaced by the harmony remote and hub (small red circle)
Back of the Harmony smart hub. This is the signal blaster that converts the remotes RF commands to IR (and Bluetooth for your gaming consoles) and blasts it all over the media closet. It does not appear to require line of sight for the IR signals. Signal is so strong its able to blast off walls to reach devices. Can't explain it actually. Just works extremely well.
Had to run a 50' 3.5mm audio cable through the wall, into the attic and down into the media closet in the first pic above. Connecting one of my old NextGen emitters to the cable's female end. Vizio TV's IR window is on the bottom left corner of the TV (the power indicator light)
The Harmony remote that makes it all possible. Blasts RF to the hub. It has no IR transmitter, which is why you need the IR cable run to the TV. Each button has short and long press action making this "simple" remote pretty sophisticated. Button's give nice "click" response, are tactile with memory contours for blind control and don't have that unsatisfying rubbery/mushy feeling like some Harmony remotes, particularly those in the 500 series.
Edited by vestaviascott - 7/19/13 at 8:56am