Tone is SOOOOOOOOO subjective so it's almost impossible to explain.
Mesa was/is cool but always sounds less open and more false, all to my ears.
The poss. to blend/use different tubes on the RK was great but it still all sounded less real and cold to my ears.
The Shiva just sounds way more ALIVE! It's like you have been transported to the studio and not listening to a CD, that kinda of realism.
The gain on the Shiva is all useable and is sooooo attack dependant it's amazing. Straight it is less aggressive to my mind than the Mesa can get but then it's 2 chan. and not a recto.
Tonewise, try this analagy (I am extemely long sighted and if you have 20/20 vision you may not get this).
Imagine wearing glasses, they correct your vision, allow you to see, but are somewhat false and limiting (Mesa) now imagine wearing contacts (maybe even having corrective surgery) everywhere you look is clear, you can wear normal sunglasses, no-one can really tell, everything is more lively and trasparent (Shiva).
Best I can do :)
But after owning, ENGL, Marshall, Mesa and Rivera for me, Bogner is the dawgs bollox :twisted: