I hope this may still be helpful, and I'm not reviving an old thread for naught.
I have this head unit in my Jeep, and will hopefully be moving into my WRX tomorrow.
My main complaint is that glare is a pretty big issue with it. During the day, I can only have the white or bright green background if I want the text to be visible at all. Other than that, it's great. I especially am looking forward to matching it's colors to the WRX, most likely red buttons with white screen, or vice-versa.
In my Jeep, I had the front speakers replaced with some mid-quality Kenwood 3-way speakers, and left the rear speakers stock. Two 12" Kenwood Tornado subs powered by a Rockford Fosgate amp (600 watt maybe, can't recall off the top of my head) and the head unit controlled everything fine.
I find it's integration with my iPhone works really well. Nearly the same as the BlueTooth / Hands Free with the WRX (HOWEVER, it DOES NOT have bluetooth music streaming, I think it's successor KDC-x996 does though).