Actually you get better sound experience in linux (ubuntu) than the windows7's. In your case this is not as I am claiming so you should find the problem in the driver or in the hardware. But if you just say "better" because of the SRS tech in the WindowsMediaPlayer well then this is another thing....
SRS, srs wow, surround and all other sound enhancing technologies are NOT FREE (actually pretty expensive, charging monthly for usage) and the Linux is a Free OS so there's no way companies providing sound experience (like the SRS) have no way to get their money, so they consider not to throw their software/hardware for free for everybody and this is pretty normal :>
I apersonally use the PulseAudio Equalizer for linux just with two simple tweaks I get better experience than the windows7's with srs_sandbox.
But if you can't fix hardware/drivers issue; PulseAudio EQ doesn't work (well) for you; and you really need to "tweak" the music you play, you could try downloading WINAMP 2.95 and running it with wINE. After that go to WINAMP.COM > PLUGINS and find "enhancer" (it's a green square on the picture with 7-8 sliders). This should give you SRS-Like experience but ONLY in the WINAMP APP.
Another (more advanced) plugin for winamp is JAMMIX which is kind'a complicated at first look, but It does the most compressing/equalizing/tubing effects like 'center' 'bass' '3d' 'reverb' 'surround' 'ProLogic' experience and so.
But at all my opinion is you should get another audio hardware (sound card)
Hope I helped