The fact that the OP is running 700X23 Vittoria Diamante Pros at 220 grams makes me think he wants a performance tire. The Marathon plus is about as far from that as you can get. It looks like 700x25 is as narrow as the MP comes and it not only weighs a whopping 580 grams, but has a very stiff sidewall that makes for a very "un-lively" ride. The ride was bad enough that I took them off after a few hundred miles. That said, some folks don't seem to mind.
So, if the OP decides on different tires something like the ultragatorskin might be more suitable.
I have no comments on the idea of liners, since I have never used them.
Nobody asked, but I will also say that I do not especially recommend heavy duty tubes and even less so for slime tubes. I have found that for me both of those have more negative impact on performance than positive impact on robustness.