For my part, I normally don't sing. But once we used my Nano 300 in our band project, and we weren't happy wih how the Nano 300 rendered our female singer's voice. Maybe we could have achieved more with an additional mixer with 3-band equalizer, which we didn't have at that gig.
But luckily I also had the FBT J5a at the gig, which I had first only connected to my synth, but when we connected both Nano 300 and FBT to the mic, the voice sounded much much fuller.
So I agree, there is something a bit muddy about the Nano 300 top speakers in some situations.