Hi Robert, Mate I would suggest you shop around.
I replaced our head unit through Monster Audio who did the install with the proper harness for all steering wheel functions and no issue whatsoever with the amp.
So even a few phone calls to other reputable audio places explain what your after and see what deal they can offer.
Everyone has their own likes and dislikes as far as head units, for me it was more music quality and ease of updates for the sat/nav system.
The other option is to do as Herb suggested and see if a wrecker has a unit available, I would use that as a last option as finding a unit that has everything you need and installing it yourself will be required.
If you do wish to stay with a stock system let me know as I still have our head-unit from our 2009 Presara which when removed worked fine with the sat/nav DVD still in it.
KAA