well, it's a mesa and you seem to use it a relatively low volume levels, i think those are your main problems. All mesas are pretty dark and a little flubby when it comes to metal playing from my experience. Low volume levels on a tube amp will always sound fizzy and a little unclear on 50w and up(the nomad is a 50 right?). Apart from that mesas have very sensitive EQs so you might need to take some serious time to tweak it.