These headphones are truly remarkable - To me...the best I've ever listened to, even surpassing the HEDD, HD800S, Meze Empyrean, 109 Pro, and ZMF Eikon. However, there's a caveat: they require EQ adjustment and the X-bass feature turned on with the Ifi Zen Can. When the X-bass feature is turned off, I increase the EQ for lower frequencies.
The headphones initially sound flat with a slight midrange boost, but they are highly receptive to EQ. In fact, they respond incredibly well to EQ adjustments without distortion or veiling of details. After some minor tweaking, I've gotten the sound signature I want.
Moreover, these headphones are among the most detailed I've ever heard. For instance, in the song "Smooth Operator" by Karen Souza, I could clearly hear the faint sound of someone's breathing at 3.5 seconds into the track. With the X-bass feature and slight EQ adjustment, even mild bass enthusiasts will find the sound quality superb, with surreal impact and quantity.
The highs are also extremely natural and detailed, without any sibilance. I tested this with songs like "Jaguar" by Victoria Monet and "Code Cool" by Patricia Barber, which sounded incredibly authentic and realistic.
The headphones are already mid-centric, so I didn't adjust much in that range. Both male and female vocals sound perfectly forward and full-bodied. The soundstage is not artificial, and the imaging is exceptional - instruments can be pinpointed not just around the head, but also in terms of height and depth.
At $399, these Avantone Pro Planar headphones are an absolute steal, but there is the catch of requiring EQ adjustment for a more exciting and enjoyable sound while maintaining the integrity of the mids and vocals.