Audio on 06 Outback Ltd

I am about to buy my 5th soobie, drooling over a 2006 outback wagon
2.51 Limited. It comes with the premium audio package which is ok, but
really not that great. What are my options? I would not mind pouring
some more $$ into it for better sound and an ipod integration but the
integrated stereo makes it almost impossible to make a good swap out.
Also, whhat are the options with sattelite radio?

Also, it does not come with a subwoofer in the 2.51 ltd - if I buy one
from subaru.autowebaccessories.com is it easy to install?

Thanks!