I'll be lurking on this one too...
My gig-rig is a Mesa Walkabout, either docked in a single Scout 15 combo-cab, or run through tandem Scout 12's. Only other thing ever in the signal path is an MXR analog chorus, or once in a bluemoon an MXR compressor. I had considered racking the Walkabout head with an F-1X preamp for a while, but the parametric-eq on the Walkabout is sufficient for this simple mind. =)
Really, the only gripe I've ever had with my setup is a nagging feeling that the mids are distorted at anything past flat response. I typically roll off a couple dB of 330-340Hz to get rid of the fuzz, and another 5 dB of 55-60Hz to trim some more phat. (Scout cabs with their passive radiators are notoriously squishy)
Not that there's anything particularly *wrong* with take-away eq'ing, but if an F-1X would help get me some more clean mids, then I'm in. I suspect my trouble is either cab deficiency or (more likely) a bad case of rabbit ears.