This is what i've heard from Harmony Central topics and sevenstring.org
The Fireball sounds different than my 5150.
I don't know about sevenstring.org but I'd be careful about any information on Harmony Central. Just my 2c.
On the BlackmoreA guitar player I knew from another band had one. I considered buying it from him at one point. I chose not to.
Not because it's a bad amp. Not at all. It's a very good amp actually. It's just not my taste.
It has the typical ENGL voicing loved by many guitar players, which is probably a bit closer to the American than the British amp voicing. But me, I like the rough and harsher British sound. The 5150 sounds a lot like a modded Marshall and it has that aggressive and hard-hitting sound while the Blackmore is more elegant and refined. That is MY OPINION after playing them both, although it has been a long time since.
Both do metal great. Both are very tight. Both will give you
scream and
chugga-chugga and
a ballsy sound, but they will still sound different. The 5150 rawer, the ENGL more elegant.
ENGL always reminds me of Hammerfall. If you know Hammerfall's sound, you kinda know the ENGL sound. The sound on the last two Machine Head album's remind me much more of the 5150.