Sonic sets the mix format (the number of physical channels) to Stereo. Most applications incorrectly read this value and output only stereo. Only if the application correctly detects that the 7.1-channel format is still available (even though the mix format is Stereo) or lets you force 7.1-channel output, will Sonic downmix it correctly to stereo with HRTF. Sonic does not apply HRTF to stereo streams. SBX works globally because the mix format is 7.1-channel. It applies HRTF to stereo streams which is undesirable. SBX on the desktop sound cards also apply phantom-channel HRTF to both stereo and multi-channel content on a multi-channel speaker system which is undesirable. Set the mix format to Stereo, disable SBX / Sonic / Atmos, and use the in-game Headphone option. This is the correct way to do it because the only the game engine knows the exact coordinates of each sound for the HRTF. If you use SBX / Sonic / Atmos outside the game, the audio is first mixed to 7.1 channels (possibly with phantom-channel HRTF) by the game engine before being downmixed with HRTF once again.