EQ usually doesn't kill the dynamic range - it's the compression and limiting that do that. Extreme EQ choices can max out frequencies though. Harmonic exciters can also kill the dynamics and the tone as well.
The bad thing about most people using EQ's is that they are using consumer based products that modify a certain cycle by using shelving controls by which the consumer has no control over the bandwidth of the affected neighboring cycles. In other words, if your using a regular EQ like those on most media players and preamps, you can boost or lower something at 1,000 cycles but you really have no idea how much you are changing the sound at 800 cycles or 1,200 cycles.
To really control the tone of a sound and make it better (or worse), you need an EQ that provides peak controls so you know how narrow or how wide the rolloff is for the frequency you just changed. All mastering EQ's have this ability and is usually labeled "Q". You also need a minimum of 3 parametric bands to really change the sound.
However, don't fear - if your using a regular graphic EQ, use it to make your speakers sound as flat as possible, as anwaypasible suggested. That usually helps a lot! Also, a little bit of gentle graphical EQ can make things a lot more tolerable. Just have fun and make sure you enjoy your music.