diplexers?

[gmbrv]

I need some advice. I have had standard definition satellite in my motorhomes for more than 10 years. I have a KVH dome on my roof and an 18 round dish for setup if needed. The feed for the 18 inch dish connects to a diplexer along with the cable input when cable is available. The signal is then split with another diplexer before the rg6 enters the satellite receiver and the cable input on the winegard selector box. I would now like to go to HD on at least one of my 3 tv's. I prsently have an HR24 with HDMI to the front tv and the component outputs to a rf modulator and the rg6 to my winegard selector box satellite in for my other 2 tv's. At present SD from my KVH dome works fine on all 3 tv's. Here comes my confusion. I have purchased a non SWM 5lnb slimline and have ordered a heavy duty tripod to set it on. Will my present wiring set up with the incoming satellite HD signal work sharing the incoming rg6 with cable via diplexers?