Great point about preamp tubes. Really can be said about ANY modern high-gain amp as the preamp stage is the critical voice of the gain stages and tone stack before the output tubes have anything to do with the rest of the tone...
I'm surprised to hear others talk of the Roadster not being "plug and play". I really feel it's the opposite. Yes, it takes SOME time simply due to quantities of knobs/switches, but certainly not to the level of a MK series.
Especially if you set it for "hard bypass" of the loop on the back, then when you go to the front, you'll have four separate amplifiers and four master volumes. And it will sound better/purer IMO.
I mean this is one of those amps that can be dialed in for ANY tone. Really. I've owned some of the greatest classic amps in the past (vintage '63 Vox AC30 top boost, '57 tweed Twin, Fender '64 Pro Reverb, '66 Super Reverb, various years of Marshall JTM45, Marshall plexi '68 and '69 100 watt, early '70s JMP series 50 and 100 watt, Soldano SLO, Mesa MK I,MK II, IV). I don't own any of them anymore and I don't miss them.
So if the Roadster is not sounding good, all tastes aside, I wonder if there's something wrong with it. Do note that any low-level in-store playing is going to emphasize the preamp buzzing with the gain turned up unless you change the e.q. a bit. That's just what preamp tubes do. Compensate for it by adding more bass and reducing presence at lower volumes or turn it up to get the amp in full bloom.
Now with all this gloating on the Roadster, it wasn't the perfect amp for me until I ditched the V30's. I know others have heard my argument about this before, but my "core" interest of tone is more of a quality Marshall style rock tone. Switching to G12K100's (which is what Diezel has done with thier amps too, so it's not just me), voices the amp perfectly where the cleans are sparkling Fender like, and the distortion has crunch with less V30 buzz and nasal midrange.
If there's a Marshall 1960B "bottom" 4 x 12 cabinet in the store to check it out with, you may find that you prefer that over the Mesa cabinet. The 1960B uses the 75 watt Celestions, not the 100's, but it is fairly close and can at least give you an idea. I don't like the slant cabs (not enough air volume for one thing and directional issues), which is why I say try it in a B-cab if you can.
But back to the original point, if they'll let you swap tubes (doubtful), then that would be a first thing to do. That and hard bypass it on the back. Good luck.
The Roadster's still on a two year honeymoon with me. That doesn't often happen with gear. I have a clip of a gained up Roadster sound with the 100's on my site under the Charvel review I recently did BTW you can check out if you'd like.
David