My cousin has that HU in his G-wagen. It' s what really pushed me into installing a CarPC.
My first mistake was getting a plain old LCD monitor. I had completely forgotten how bad my desktop looked when I had it connected to my 27" 480i TV. I quickly remembered after plugging a 7" LCD monitor to my computer and the only thing that looked barely decent to view were movies. After that, I bought a Lilliput* with touchscreen and never looked back.
You need to get an LCD with VGA inputs. The AVIC has just a basic LCD TV with a touchscreen. 95% of the people here use either the Lilliput or Xenarc LCD.
*-Some of these monitors come under different names. I bought a Starvision branded LCD that looks identical to the Lilliput and has all of the same shortcomings, except that I haven't had any problems. Search the LCD forum and you'll find tons of posts concerning the good, bad and the ugly on these very important components of a CarPC.
P.S. He hasn't seen my setup yet, but I'm sure he'll quickly regret his $2000 purchase.