Ive had an extended listening session with the se300, comparing it to the sp1000 (using u12t- mainly, Monarch Mk2, Fostex th610, Meze Liric).
I loved it in general. Great soundstage width, great dynamics and very deep bass.
But to my ears, it wasnt as refined and full as the sp1000. Tbh, the sp1000 sounded warmer and more analog, with even better separation and more pronounced layering. Vocals on the sp1k sounded like they were in their own bubble, each instrument had its own very precise place on an imaginary stage. The sound was also slightly fuller and more rounded, with less sharpness. The stage wasnt as wide (still very big, on some tracks even bigger) but was deeper, more holographic and complex.
The se300 sounded more fun and aggressive, closer to my face and sharper. The vocals where more blended with the rest of the music and the tonality had a slight paperish flavor. With all mentioned iems and headphones the results were very similar.
But all these conclusions were drawn only after direct comparisons. As a dap the se300 is an amazing sounding device, very dynamic and fun. It also has this typical R2R soundstage, which is very wide and spacious. IMHO is better and more interesting than the sp2kT.