I'm not sure how much $$ we're talking here, but I would assume the WRX unit isn't cheap.
Anyway, have you looked at Nakamichi units. Single din, 6 cd changers, understated appearance.
OEM site here:
http://www.nakamichiusa.com/auto/mus...b_75_specs.htm
For sale in the US here:
http://www.thezeb.com/caraudio/nakamichi.html