Someone else could probably give you a more technical description of the difference, but I noticed your post was falling toward the bottom with no response so . . .
The RES system is a DVD based system not VHS. It is the only entertainment system available as a factory option. We have it and, I think, it's pretty neat. The controls are nicely integrated into the dash which I like both for convenience and looks. In order to get the RES, you have to also buy leather so if you would not get leather anyway, you are looking at an additional sum that I believe is in the neighborhood of $3,000. But we are gadget freaks and I am glad we got it.
The IVES is a dealer installed system that is VHS. I don't know much about it. I also assume that the dealer could install a DVD based system, but I haven't heard as much talk about that and it sounded like you wanted the VHS system. Someone else can probably tell you the cost of this. Maybe my reply will bump you to the top again and someon else will lend a more expert opinion.