The IRV66 has two additional HDMI cable inputs on the rear of the stereo. By plugging in your HDMI cable input to that allows you to play the sound and video thru the IRV66 stereo.
Now, if you haven't replaced your IRV66 (if you have issues, I highly recommend you get it replaced with a new updated version) with that said, to remove the stereo you first need to remove the face plate, towards the bottom there is two slots that a small flathead will fit into. start from there and work your way around until it just pops off. Next 4 Phillips screws should be holding it place. remove those and stereo will just slide out.
The HDMI input is on the very top. Be sure to plug into to the input as there is two outputs as well. I hope this helps.
****info on replacing IRV66 found on this thread (see post #156)....I RV radio