Has anyone tested the s12 with a&k pee51?
I use my S12 original (no mods) often with my A&K Pee51. With the 51 connected to my Windows 10 lap running Foobar2000, the S12 can be pushed upwards to 25 - 30 (quiet tracks, older more dynamic recordings), anywhere past that is too loud. On modern compressed music, 16 - 18 is often too loud. With other non-planar IEMs I have, the volume is usually anywhere between 4 - 16 on average depending on the track and how loud I feel listening. Volume is not an issue with the S12, so no worries with that.
Tonally, as a pair-up, I'd be careful with ear tip selection. I use Symbio W with my S12 now and the 51 and it is decent enough for longer listening sessions. The 51 seems to lean toward brightness, albeit in a good way, and the S12 original is bright too. I do remember the S12 being intense with Spinfit CP145 and I couldn't listen for too long without needing a break.
Agree with @rayliam80 .
I think the AK PEE51 shares the AK house sound which is a bit on the bright/edgier side, and the S12 is already quite bright in the treble, so personally I'm treble sensitive and find that they don't synergize that well. YMMV, cause we have different eartips, different hearing health, and play at different volumes (fletcher munson curve).
Eartips that tame treble will help for sure, if you wanna use this combination.