Well for tweeters, you can get the sail panels (the triangular pieces behind the side rear view mirrors) frpm an 03-06 XRS which came with the 6 speaker system. You could mount any tweeter that fits then.
As for the indash NAV system, The Pioneer Avic 3 is great HU with IPOD and bluetooth and has the NAV system as well.
Whenrepalcing the speakers, it's a little tricky, especially the mounts and make sure they aren't too thick so that the windows don't hit them when rolled down. Good luck.
Oh, welcome to the site. There's all the info you'd ever want and more at
www.matrixowners.com