If you don't already have the factory navigation system don't bother. It is nearly impossible (and *very* costly) to convert a non-navi model to factory navi. You need more than just the screen and DVD player to make it work correctly. Also, since stolen navi units are a problem on eBay, if the seller doesn't have or give you the code to activate it once installed, you're going to be stuck with a non-working unit as Acura will not give out the codes when they cannot verify from where a unit came.
You'd be better off to get an aftermarket navi like the Garmin Nuvi or something similar.
As for the AM radio stations, AM reception has always been weak on the 1st gen MDXs. You might be able to install an aftermarket antenna but I don't think it will help much. An aftermarket headunit with better AM sensitivity would probably be a better choice if you really want AM radio.
2005 BSM MDX w/navi