I am assuming you are getting the sound from your SoundBlaster Z soundcard? Have you made sure you have not have the surround or other effects switched off?
I have the T40 II along with Monitor Audio BX2 and Q acoustics 3010. Whilst the latter 2 are better, I don't think the T40 II is as bad as the way you described it...something much be amiss. Have you already tried turning down the bass dial on the T40 II, rather than having it all the way up? For my T40 II, I turn the bass dial down to around 40%, as I feel that the bass as default (50%) is affecting the mids and highs of the sound slightly. I would advise play around with the bass and treble dials a bit before making up your mind.