I second the guy who suggested digital processing ala Room EQ Wizzard. I'm a renter who's had to deal with all sorts of terrible-sounding rooms, and room correction is an absolute lifesaver.
I currently use MathAudioRoomEQ via Foobar2000, but there are hardware-based solutions that are a better fit if you have analog sources.
I currently use MathAudioRoomEQ via Foobar2000, but there are hardware-based solutions that are a better fit if you have analog sources.