I just auditioned the Onkyo HF-300 headphones. It was a short ~5 minute listening session as I was in a bit of a rush, but here are the main bits, in comparison with my Don Scorpio Dolphins:
- Bass quantity, particularly sub-bass, seems to be larger. Definitely hits harder
- Sub bass texture seems its strongest suit, best out of any headphones I've tried so far (admittedly not a lot)
- Mid bass is decent
- Mids are moderately recessed (but not too weak) whilst the DSD can't really be said to be recessed at all
- Treble is very smooth. Zero hint of sibilance. Might be slightly more extended
- Very clear sounding
- Detail is above average
- Soundstage is impressive. Width, depth and height are all present.
- Isolation is good
- Fit seems to be for smaller heads. May be tight clamping force for larger heads
I wished I had more time with these to have a better gauge as to how much I liked it. I consider myself to be bass adverse, but I must say this was one of the only headphones thus far which has actually made me focus and appreciate on the bass rather than the higher frequencies.
I would place it very close to the DSD in overall ranking, but just a hair's breath lacking. Do note I did not have an amp with me, whereas I've been using my DSD with my Fiio E07K almost all the time.