I'm looking into investing in a high-end head. I've played on friends
Mesa Boogie Dual and Triple rectifiers before as well as a Soldano
SLO1000. Characteristics that I'm looking for are very rich and organic
cleans; I have a hollowbody Carvin Holdsworth sig that I use for my cleans.
I have a Carvin DC400 mahogany body/maple top/maple neck that I use for my leads, and as my primary guitar
I don't need anything really in the middle such as a light crunch, or fuzz.
But I do want a very tight, smooth, and harmonically rich overdrive to play
leads with. I mostly play leads in terms of guitar playing; I like fusion as well
as just regular "shred". I don't do much metal riffing, but I want a tight low end
for when I do some riffing. Over all, I mostly play fusion (Greg Howe, Di Meola, Govan, Holdsworth, Sfogli, Gambale, etc.) but with more gain than the aforesaid guitarists. I also play metal; usually technical death stuff like Necrophagist, not much in between, then some of the more stuff like Ozzy, Racer X, Dream Theater (LTE), Symphony X etc.
Amps i'm looking into are the Hughes & Kettner TriAmp® MK II, VHT Sig X, some kind of Mesa Boogie, or maybe an ENGL. I haven't had a change to play any of these (or any other high-end amps) except Mesa Boogies, which I like, but I might keep looking for something better.
Disregard price, but naturally, lower is better. Also, don't compare the aforesaid amps to each other, perhaps to other amps within their perspective price/quality range.
Any help in deciding would be extremely helpful.
For me, it was between a Dual Rectifier and an ENGL Powerball. I am into tight death metal riffs, and smooth shred, as well as clear high leads like those of Blind Guardian and Kamelot. The ENGL totally nailed it for me. Excellent low end for heavy riffing and gloomy cleans, just the mid that suits my ideal shred sound, and an extremely clear high end. Comparing it to a Dual Rectifier, it just appeared better to me in every way. The ENGL feels very much alive in terms of sound. It's not cold and industrial, although you can certainly make it sound that way if you want to, but rather smooth and powerful. Hard to explain the characteristics of an amp in extreme detail, but the ENGL just got me there instantly. Also, the noise gate on that thing is incredible. By far the best I've tried. Set it to max and you will have a very hard time getting feedback, even if you try. Naturally, it all comes down to preference, but I'd give the Powerball a go, as it is a great amp with lots of versatility. There's not a style you can't match, although the more heavy aspects appear to be what it is originally designed for.
Try a Rivera Knucklehead Tre and a Laney VH100R before you make your choice. The Tre is a very harmonically organic amp and sounds excellent on both channels. The cleans are superb for a high gain amp.

The VH100R is more of a Marshall type of amp with a smooth overdrive and also a very decent clean.
I'd say the perfect amp for your style would be a Mesa Boogie Mark IV.

You could also check out more botique amps:
Framus Dragon
Framus Cobra
Diezel Herbert
Diezel VH4
VHT Pitbull or Super Lead
Bogner Uberschall
Krank Krankenstein

honestly Mesa Boogie Dual/Triple Recs don't compare to any of these amps.
Ibanez PGM100
Taylor 314-CE
Peters Chimera
Orange PPC212 w/ Celestion V30 and Celestion G12-75