I have the triaxis and quad preamps
Basically, the studio is 50% of the quad preamp. Sp the Quad will offer you an additional channel to work with and 4 modes total versus 2 modes total on the studio
So far, I think the quad and studio pres are best described as rackmount preamp sections of the mark 3/4 amps.But Mesa feels that the studio and quad are based on the Mark 2C+ and Mark 3 sounds
The triaxis is very much based on Mark 3 and 4 sounds as well however it is colred by all the extra gizmos in the circuitry like op amps and such. So while sounding fairly similar to the quad preamp, the triaxis also sounds and feels alot more compressed.It's definittely not as snappy as the quad and sounds less amp like or less organic.
The major thing here is that the triaxis is midi controlled and offers lots of neat functions like switchable effects loop and 3 relay output switches.Aside from that, the triaxis version 2.0 and 2.01 offer a Recto mode which offers a little different kind of sound. It doesn't sound like a Recto though.But it's there if you ever need it.
I havent' tried the formula but hear it has a good clean tone
As far as power amps, you have alot to choose from. The least expensive are usually the Mesa 20/20 and 50/50 .
Mesa 20/20 EL84 driven and sounds nice with triaxis.It's really light and has enough power to drive 2 cabinets without breaking up alot
Mesa 50/50 Four 6l6's inside . It has plenty of power and sounds fairly transparent.I enjoy running my quad preamp through my 50/50
Mesa 2-50 Similar power to the older 50/50 but is said to have a deeper sounding low end response and a spongier feel. Looks pretty too
Mesa 290 Eight 6l6's in here. Rediculous power and headroom. I owned one ofr a few years and found it to sound good. I never had any use for the extra voicing features. The Deep mode generates alot of noise and my triaxis has tons of bottom end anyway. It doesn't require a deep boost at all.But hte voicings are there if you want them for anything.Half power mode sound cool but works the power tubes really hard.Use the amp in Half mode alot and you'll be changing tubes more often.The 290 oes have some problematic parts. One such part is hte input slider switch. It's a cheap slider switch and when it starts arcing (and it will) it will screw with your channel volume and tone.It usually causes the volume to go up and down all over the place.Otherwise, the 290 has some pretty solid tone.
Mesa 295 Really cool power amp that is simulclass and will run 6l6 and El34 tubes at the same time.this is veyr cool in my opinion. By the way, the 290 power amp can do the same thing. Mesa doesn't make it anymore but it's a great sounding power amp an might be Mesa's most versatile power section.it isn't as huge as the strategy series amps but still does some of the cool vibe that those amps have
Strategy series Haven't played one yet but I've heard them. They are great sounding power amps but are massive in size. Way too big and bulky for me to want to buy one. But aside from size, they are great amps.