**The Amazing: Truthear Hexa**  
This is the absolute golden pairing. The Hexa is famously flat and can sometimes feel a bit cold or boring. The M3 Ultra gives them exactly what they’re missing. It punches up the sub-bass, adds a ton of warmth to the lower-mids, and makes vocals sound intimate instead of clinical. It turns the Hexa into a super fun, musical daily driver. No hiss or background noise either. Love this combo.

**The Not-So-Good: Fiio FT1 & Letshuoer S12 Ultra**

* **Fiio FT1:** This was a miss for me. The FT1 is already a pretty warm, bassy dynamic headphone. Stacking the tube warmth of the M3 Ultra on top of that just turned the sound into mush. The bass lost its texture and everything felt way too dark and congested.
* **S12 Ultra:** I didn't love this either, but for different reasons. The S12 Ultra has that fast, intense planar treble. While the M3 Ultra did smooth out the sharp peaks, it also softened the overall attack too much. The planar speed felt blunted, and the treble just sounded weirdly rolled off rather than naturally smooth.

**What about the Hifiman Edition XS?**  
It gets loud enough on the 4.4mm balanced plug and rounds off the sharp treble nicely. But let's be real—the M3 Ultra doesn't have the desktop juice to make the bass hit like it should on these power-hungry planars. Good for casual couch listening, but it won't replace a proper desktop amp.

Tubes on the go...Muse Ultra M3 Ultra