There are a several options for "clean" pre-amps... for that matter, "clean" is it's own color. Much like there are about 4000 shades of white at the paint store there are 4000 shades of "clean" when it comes to mic amplifiers.
In the amazing world of "clean" I have found the Millennia to be an amazingly boring version of the species... the GML, the Martech, the John Hardy all have more soul and depth. There are even tube based units like the DW Fearn, the EAR, the Pendulum MDP-1 that are exciting and [dare I say] "sexier" versions of "clean".
My current favorite bit of "clean" is set to come out in a couple weeks. It's made in Atlanta by a company called "NPNG". I've been dicking around with the proto-type for more than a year and have to say that I've never experienced "clean" like this "clean"... it is a very "deep" sounding "clean"... a "clean" with size, a front, a back, a depth and a definite soul.
The Millennia specs better than anything I've ever heard about... my only problem is that I don't record specifications, I record music... so while there are many [MANY!] who seem to feel that the HV-3 is a great pre for their applications in "clean" world, I find the thing damn near useless as it brings nothing to the table to make my music more exciting.
As always, YMMV.
Peace.