The S12 is a V shaped set with big bass and boosted treble.
If you are treble sensitive, the treble/upper midrange might bite a bit. It can be tamed somewhat with playing at softer volumes (fletcher munson curve), using treble attenuating tips (eg foams, Final E black tips), or even with warmer sources. You can EQ the upper mids/treble down too.
The planar timbre can't really be gotten rid of via EQ solely, it is an inherent characteristic of most planar IEMS, where the very fast transients and rapid decay gives notes a thinner weight and a less natural timbre. But the S12 has one of the best technicalities/resolution at its price point, compared to say single DD types with better timbral accuracy.
Agree with you here. Very competitive resolution for the price point but tonally and timbrally quite unnatural. Foams/narrow bore silicone, cable changing and EQ can help but you're still dealing with a planar driver that prioritises resolution.
I'm hoping Shuoer will release a V3 with a fresh approach to the treble and a change of stock cable. The Chimera (I think that's what the stock cable is called) is highly resolving but leans sharp and bright and wouldn't be what I would personally throw in with an already aggressive V shaped IEM.