FiiO K9 Pro ESS mainly considers the needs of headphones, so the sound tuning is based on resolution. Moreover, we do not pursue strong tension to express his driving power. Coupled with the blessing of THX, the sound reproduction is relatively high, and the background sound is clean; the soundstage is regular (longitudinal and horizontal are regular) In addition, due to the high magnification and strong driving ability, when matching different headphones, please pay attention to matching gain and volume. Although they are all headphones, some have high sensitivity, you can use medium gain + large volume for them which will make the sound softer and more delicate.If the sensitivity is low, it is recommended to use high gain + loud volume to get sufficient power.