ime plinius are on the darker side of neutral, as are the top ayres (less so than plinius, but still...)
krells, mccormacks (smc modded ones) have more extended airy treble but can be a little revealing on less well recorded material
most pass labs amps and accuphase have quite extended treble but add some warmth to the midband and midbass
top hegels, classe, belles class a, exposure, and certain first watts are most balanced in sound, not lean not rich not bright not dark
devialet and agd are a somewhat different breed, saturated yet very extended, ultra smooth, devialet a bit more colorful and forward, agd is fast rich silky smooth