Some soundcard drivers apply equalization by default or strongly suggest it via features like "gaming" or "cinema" modes. If your setup previously had anything like that, then changing can be quite noticable. One tends to develop a preference for what one is used to listening to. EQing according to ones own preference can be very beneficial in audio experience. Most OSed have ways of doing it globally, potentially with this party software.

PS: see also the comment from Ross about the drive ability of your card