I'm not really sure of them. I'm all over the place and haven't really give equal listening to them.
love the KC2 for vocal. sounds really nice even at lower volume. I have been using this for longest time and used to their signature.
I also like the topaz vocal although the treble is less exciting compared to KC2. The female vocal don't have that shoutiness that other IEM can have. I'm not sure but I think it sounds somewhat more natural compared to KC2.
The T3 plus I need more listen before I can comment on them. Best fit, ergonomics and isolation though.
E3000 at first I don't like them feels like lacking details but I comes to appreciate them now. They may feels muffled compared to others if I listen at my normal very low volume. Higher volume makes them feels better but usually I don't listen too loud.
SG01 a bit exciting and very easy to drive but when I listen to other IEM they did lack refinements.
Tanchjim zero sounds better using final e type tips.
I look more for iem that balanced male and female vocal so that duet don't sound off. Something natural sounding.
I am not sure what genre I listen to. Maybe folk and singer songwriter stuff the most.
Genre I don't listen to is metal, EDM hip hop.
Some of the artist I listen to now is Leonard Cohen, Johnny Indovina, Johnny Cash, Sivert Hoyem, Nick cave PJ Harvey, Tamino, Katie Melua,Sophoe Zelmani, Suzanne Vega, Joan Baez etc. The list always change but I usually don't like noisy, incoherent music.
I guess your IEM diversity with that “male and female duet to be equally balanced” part a hint where you may find the ideal curve for.
I’d suggest qdc tuning.
The best you can reach is Anole VX, mid budget options (DUNU SA6 ($560 )& SA6 Ultra (already sold out for $599 as it was 300set limited collaboration item). If a little bit more engaged, See Audio Bravery (OG $279, new shell around the same price)—still one of my endgame for vocal-oriented genre. It’s a bit high In hurdles, but I see a startup in Singapore (Aur Audio) makes Bravery on steroids,Neon Pro for $650. Someone have extensive experience mentioned if properly amped Aur Audio Neon Pro is par or above Anole VX (I’s take it because of slightly spiced up tuning of Neon Pro like Bravery has)
My understanding for qdc tuning is U-shaped with equal mid-uppermid plateau. This will bring you both excitement and equally balanced male /female vocals.
There is a budget option for that tuning, TRI’s Starsea.
If you are seeking more balanced tuning, You may hit Mangird Tea (OG) or AFUL Performer 5, both has very flat expressions across vocal range.
Tea (current $239) is replaced with XENNS Mangird Tea2(299), much smoother feeling of Tea2, in exchange of loss in male vocal range information density. Tea is 6BA+1DD 3 way design. It has TOTL class mid range, as they’ve spent 90% of their budget in midrange. Backed by 4BA of Sonion 2600, totaling 8BA left/right for vocal range, I have to emphasize Tea OG is vocal-beast.
For AFUL P5 going at $220, it has simple 4BA+1DD popular config, 2BA as tweeter, 2BA for mid, 1 DD for subwoofer. The mid-upper range is extremely neutral, but still enjoyable. What makes P5 special is speaker-like thumping subwoofer, which will add realistic touch to baritone region of which male vocal will gain benefit.
Also
@baskingshark mentioned, HEXA is very vocal-neutral as well, with best cost to performance you could reach. A great option to bet. And it’s $79, a fraction of what the other options are offering.