Probably a driver issue, there should be a button to the right of the preset dropdown box to switch to manual custom tweaking. You can also access the EQ from the control panel from the output device properties and I found that place to be slightly more accurate (allowed finer steps of adjustment). But should be said, Realtek's EQ is quite horrible quality wise, you should stick to like steps -/+ 3 at most, anything more drastic and it starts to color the sound in an unwanted way.
At least that's my experience testing many different EQ's from parametric to 10-band EQs of various soundcards or VST software EQs, the quality does differ quite a bit. They may have the same task/goal but how well they execute that task seems to differ quite a bit. In best case scenario, the EQ should just be like a "loudness tweak" at x-frequency range but often there is sideeffects going on which shouldn't be happening.
The best 10-band EQ I've used for example would be the one in the kX Audio drivers for Audigy cards. It could even apply up to like 3-5 EQs in succession and you could boost the bass by say 30dB or whatever silly amount and it would still sound clean, it just made the frequencies louder (of course you have to watch the output volume doing so :P)
Edited by RPGWiZaRD - 3/11/13 at 6:46am