I am using Realtek's driver without an issue. Listed below is what I would try. Some of these suggestions may seem elementary and moot so please bear with me.
1.) Go get an accurate meter. I use VU Meter v1.2. It's free at vuplayer.com. It is "VU" as opposed to "Peak", but any recording that's worth it will play just fine if you keep the levels "in the black". The other advantage of this program is that it truly monitors your levels after all the processing you may have in front of your audio card.
2.) Open your favorite playback app, i.e. VLC Player, MS Media Player, etc. Disable all audio compression in the app. (With VLC, that would be Ctrl+E>Audio Effects>Compressor. Not sure about WMP. Have not used it in a long time.)
3.) Open VU Meter, right click on display and choose "Always On Top". Adjust audio level, at the player app, so that meters read in the black. I've found that on my system, I can hit +3 with no problem. Any thing over +3 and you will run into digital compression. That's an infinity to 1 ratio as all the bits turn to one's and there's no where else to go. If this is your problem, then you're done. If not read on:
4.) Open Volume Mixer from the quick launch area. choose your output and click on it. I'm just using speakers so I click on "Speakers". In the "Enhancement" tab, check "Disable all sound effects".
Different source materials will have different volume levels (even from one video/audio file to the next) depending on a variety of factors, therefore for the best results I always consult VU Meter when opening a new file. If it interferes with viewing a video, simply close or minimize it after setting levels. Once again, as a rule of thumb, you'd want to keep it "in the black", but do not reduce the level excessively. Too low a level and you will loose audio resolution. Minor excursions "in the red" is acceptable unless you're a studio engineer.