http://www.manualslib.com/manual/258313/Linear-Rv5055.html?page=27#manualIf this is the same unit, there is no HDMI and it lists only a Composite connection (optional game console) and a USB iPod connection. It appears the DVD is just inserted in a slot. If that's all correct you will never get high quality DVD. You can you see only one grey wire to the back of the TV. Where does this wire connect? To the Coax TV IN or some other port?
I assume you are actually doing a scan on the TV and that's a function of the TV which you can do nothing about other than replace it with a different brand. The secondary scan will likely then be necessary to find the DVD but you should have the option to do a scan for additional channels (or similar wording) as opposed to a new scan. This way you can turn to the DVD option and do the secondary scan and you would have both the locals and the DVD channels available. This only has to be done once at each location and you are good to go.