I've never played an elmwood m90, but I have quite a bit of experience with the Nitro. I owned a KT77 one for a few days and my band mate has a KT88 loaded one know. I think it comes down to what you want out of this purchase, but it sounds like you're gassing for the Nitro.
IMO the Nitro isn't an ultra versatile amp so it's appears to be the polar opposite of the elmwood. It can get some very crushing modern metal tones and honestly I've never heard an m90 clip that has impressed me with those types of tones. All the clips I've heard always lead me to believe that if there was a genre of music the M60/90 isn't suited for, modern metal would be it; there is a common quality I hear in the clips that just doesn't seem like it would be pleasing to do that stuff. I know Soilwork uses them, but I recall someone on a thread saying their live sound was a bit muddy and fizzy. Just one opinion, but worth mentioning. One the flip side, some of the best lead clips I've heard were on an M90 and the M90 boosted clean clips sound killer too.
I've also come to the conclusion the Nitro is very picky in regards to guitars, pickups, & cabs/speakers. I've heard it's best to stay away from V30's with the Nitro. I'm starting to see why. With V30's it's very hard to find the right guitar and pickup combination and dial in a very tone. If you do, leave it and don't touch it lol. Again it's not an ultra versatile amp. It has a prominent low mid voicing that is present and you probably won't stray to far from your tried and true setting. The clean is also ok, but not spectacular.
I will say what I've said about the Nitro 100x before it's loud and the master sucks. My band mates is better than mine was, but you won't want the amp if you're jamming in an apartment. You got to open is up some.
I personally wouldn't own another Nitro. I think there are other amps that can do those types of tones much better & with more character, though they're probably more expensive. However, if I wanted monstrous metal tones I've never heard an elmwood clip that would make me want to try one out for that stuff. So I guess back to my question, what do you want from this amp purchase???
