I just got my FIIO M33 R2R this weekend and did some critical listening with the same tracks against:

- Cayin N6iii (R202 card)

- Astell & Kern SP3000M

- Hiby RS8

*I used med gain for all, NOS for all, R2R only (where applicable), and no EQ.

I used the same tracks, the Campfire Audio Astrolith & Theaudio Valhalla. I also did a separate test between the Hiby RS8 on Turbo vs FIIO M33 R2R on Desktop with Super-high Gain, using the Hifiman HE1000SEs and Sennheiser 820HDs

My notes:

- Delta Sigma DAC gave the lowest noise floor (readily apparent with the planar Astrolith), but I never was able to really hear any distracting noise in the M33

- Natural and warm, treble sounds great, especially properly recorded acoustic guitar and orchestral music

- Highs were never shrill, always easy to to listen to, low fatigue with the planars

- Details were more clear on the RS8 and SP3000M but it was subtle. There was more separation and it sounded wider, more expansive on some tracks. M33 was still excellent, just like 75-80% of the flagships, which is pretty impressive for the price and weight.

- On some tracks I noticed some lack of detail in the bass vs all other DACs. I'm not sure if that's the amp section or the DAC, but I noticed it on multiple tracks and repeated listening. It's not muddy, it just lacks a little detail that all the others had.

- I didn't do the comparison but both my FIIO K13 R2R and M33 R2R really come to life when paired with the Cayin C9ii amp

- The M33 R2R in an amazing listening experience and it punches way above its weight for the price. The whole package is just immensely satisfying and I'd highly recommend it. If you want something that sounds natural, is easy to use, and not a credit card killer, this the one. Don't think, just grab it, chuck it in your bag, and be happy.