I had another chance to listen to the Ollo S4X. What a beautiful headphone it is. Very neutral like the Planar, I did find more extension into the sub bass on the S4X but the Planar was overall more neutral throughout the mids and treble with more treble extension. I felt imaging was more precise on the Planar but the S4X was very good. Soundstage easily goes to the Planar. The S4X had great depth but the Planar felt more airy and wider in comparison. Detail also goes to the Planar same as transients and speed. Dynamics was close but I think the S4X had the upper hand. Overall, for me, I personally like the Planar more, with a low shelf at 80hz of 3db it also helps fix the roll off and I feel the planar can give more low end detail as well. For build, the Planar is all metal but I actually really love how the S4X felt. If I had to choose one of the two though, it would be the Planar hands down. It's basically a more mature and refined S4X in a Planar driver