Foobar2000 can play DSD256, but whether you're getting native DSD playback or converted PCM depends on your output settings and audio hardware. Since you're using your PC's onboard sound, check whether Foobar is converting DSD to PCM before sending audio to the sound device. If it is PCM output, you can still customize the sound with Equalizer APO. For more details on Windows audio settings and equalizer configuration, visit this website.