We just got back from our inaugural trip in our 38EL. Like you, found the Tv set up to be 'interestingly dated'.
Apparently, Jensen is unaware of BluRay as you can't get one from them and they don't provide that feature in the JWM9a. Other things I noted.....
The HDMI on the wall is your HDMI 2 input. I use it for my bluray player.
Cedar Creek connected the RCA audio IN cables (red/white) to the Composite INPUT connections. On our Tv there are no red/white RCA audio out. Only optical. So no sound from the Tv thru the stereo....yet. Got to install the optical cable.
There weren't any electronics for the Jack antenna on the antenna itself. Cedar Creek wired it like a Winegard. Each time we want to watch OTA Tv instead of cable or satellite, I have to push the power button on the Tv connection plate behind the Tv. Major PIA.
2017 CC38EL Silverado 3500HD