I've searched/read all the post's on here about empeg's in WRX's and I just want to make sure there isn't anything that they are going to run into thats abnormal from a normal deck install!

Surely, then, you've read that the scooby dash bracket is slightly too narrow for aftermarket stereos and needs to be trimmed (among other things) to get the stereo to fit? Have a closer search through the BBS posts, making sure you've set all of the search options carefully. There have been many threads on WRX installs, which detail very clearly how the owners worked around these issues.

Also look at the photo gallery at riocar.org, there's more than one set of pictures of scooby installs that detail the procedures needed. You might want to print out some of this information for your installer in hopes that he doesn't rush things. Trimming the dash to fit is exceptionally tricky, and it's not something I'd trust the grunts at Good Guys to handle properly.

Also, the empeg requires an outboard amplifier or a second head unit. That makes it something abnormal right off the bat. Plus, Mark1s need a special set of grounding leads to be properly installed. These things are coverd in the "Car Installation Questions" section of the FAQ, have a look there.