You can find detailed information on audio bit-depth here. Open Windows Sound (right-click on Windows Volume tray icon-> Sounds or if missing type in Windows search: 'change system sounds '), select Playback tab, double click your default playback device (for example Speakers ASUS Xonar Audio Device), go to Advanced tab and in the Default format entry select 0 Hz (studio quality) as shown in this picture. Windows Vista/7/8/10: Setting the Windows audio playback to 24 bit will slightly improve audio quality.

You can read more on the impact of sound effects to DPC latency here. They also change the sound not always in a good way, you might like it for your music but it might harm the audio positioning in games. The effects will increase the DPC latency, which in turn could cause other problems like audio/video desynchronization or slow network/internet speed. I'm not aware of an option to control the output impedance being available in C-Media Panel. In XonarSwitch this is available under Headphones Gain. In ASUS Audio Center click the Hammer icon to select a different output impedance. Headphones AMP (impedance) options are only available when Analog Out is set to Headphone. Do not set the impedance much higher as it may damage the headphones.

If your Xonar card has a dedicated headphone amplifier, set the soundcards output impedance/gain ( Ω = ohm) to a value close to the headphones input impedance (look for it in specifications, data sheet or manual).

GX is responsible with emulating EAX effects in some older games, but it’s know to cause crashes, audio loops in games and BSODs while it's enabled.

If you have 2 speakers and a standalone subwoofer that is connected directly to the audio card check this guide.

If you wish to emulate 8 channels surround on 2 channel headphones, set the number of channels to 8, analog output to “Headphones”, enable “Dolby Headphones” and “7.1 virtual speaker shifter”.

By default, selecting more channels than the number of speakers you have connected won’t enable you to hear more sounds or hear the footsteps and positioning of enemies better in games.

For a 2.1 audio system, select Audio Channel to 2 and Analog Out to 2. For a 5.1 audio system select Audio Channel to 6 and Analog Out to 5.1. Select Audio Channel/System input (present only in Win Vista, 7, 8, 10) and Analog Out/System Output settings based on the number of speakers that you have.

Increasing Sample Rate without having a source that’s sampled at a higher rate won’t improve sound quality, in fact, it might degrade it. Set Sample Rate to 48 kHz, this is generally good for most media (games, movies, music) which is sampled at 44.1 kHz, while video DVDs and Blu-rays and some of the Hi-Res Audio music have a sample rate of 48 kHz.In sound card application settings (ASUS Audio Center, C-Media Panel, XonarSwitch):

Xear audio center c media 3738