I think you did the right thing with the Sony Blu Ray Home Theater, saves you some space and wiring and all to not require standalone powered subwoofer.
For HDMI and using that over existing coax there are baluns that convert HDMI to coax. So if your RV has coax runs and you want HD to be sent you can use them. They are a little bit pricey
Another option is to use wireless the new standard 802.11ac which is faster than wireless 802.11n to distribute signals, you can possibly use baluns on that also.
I would prefer to transmit video using ethernet throughout the RV and the house for that matter.
Keep us posted on how things are going, oh and one question, how are you securing the components in that cabinet so they dont slide around?
