So are you looking to try and put the stock subaru stereo back in?
You'll need to take out that aftermarket install plate/surround. The stock metal bracket bolts in and the stereo bolts to it. It's possible that bracket is still there, but you may need to go to a junkyard and scavenge what you need. Usually most junkyards have already pulled the stereo. At least they do here in the states.
go to halfords or any good car parts store and ask for the iso plugs for the stereo i have the same car but mine is the 2.0 estate awd version and i had to put a cd player in it quiet easy with the iso plugs
Wow, that's the stock setup you guys got?? Sweet... Headlight leveler switch and all. We got a crap 1.5 DIN cassette player and a storage pocket that nothing useful fits into.
You should be able to fit any aftermarket stereo in there, just order the adapter electrical harness for a Subaru. Plug and play into the car harness, but you must splice it to the new stereo's harness. 20 min. work.