Is a regular Ceriatone Expression able to get tones as great as those:http://soundclick.com/share.cfm?id=9925235 To me that's the way it should sound. Of course the amp will need some kind of attenuation to get this level of saturation without playing freakin' loud!

Which kind of attenuation is the best for the Expression?  external power attenuator or internal Hall VVR??

So you're saying that the Expression cannot sound good with any kind of attenuation...?

My basic use will be for rehearsals and gigs, but of course being able to play it at home too is a +.

I got an Expression with VVR and master volume
For me, the VVR adds nothing useful
The master vol works quite well
6v6s sounded lame when I tried them

As far as I can see, the magic of this amp is that it plays clean when you dial the guitar volume down. Not that much use as a trick for most people.
The tone is good, and if you like Marshalls it's a better version of that 80s sound than any Marshalls I've tried (which is not all of them)

I preferred to replace some of the preamp & PI valves to get a better tone and slower breakup
You will not be able to get a good tone from this amp quietly,unless you invest in an Isolation Cab
The THD hotplate and Marshall powerbrake were not good enough for me.
Some people like power scaling or VVR or hotplates. I bought them all. They all suck tone. tbh a dummy load and a speaker emulation from Amplitube 3 does better (I've tired this)
If you need quiet, get an ISO Cab.
The Randall one is not as quiet as you might want, but sounds great. The Axetrak is very quiet but needs a lot of EQ and doesn't work for everything.
Pretty easy to get one built for yourself though.

Cheers
Tone

How can it have the same characteristics and be lower wattage?
Is it a 2x EL84 model?
If so, aside from all the other circuit elements, EL84s do not sound similar enough to EL34s
I just sold a Cornell 18w Plexi - to me it sounded nothing like the Ceriatone JTM45 I had bought subsequently, so I sold the Cornell. Lovely amp, but not the sweet spot of the sound in the JTM45

Cheers
Tone

I hope there is a way.

Trouble is, the reproductions Nik sells are based on those amp designs that, out of the thousands of designs made over 60 years, have proved the most enduring and popular with guitarists. These are almost all push-pull designs based on 6v6, EL34, 6L6, KT66 valves or similar.

I have bought 8 low-powered valve amps. Only 2 of them sounded good, none of them sound as good as a JTM45 or a DC30, etc
You are entering a market where there has not been 60 years of competition and refinement, most of them are the first or second low-powered design from the builder.

To me it is not yet proven that you can get the tone of the best high-powered amps with the low powered ones. They are getting closer, but there are  obstacles:
1. Each valve type has its own tone
2. push-pull sounds different, but doubles the power
3. We are still at the early experimental phase, there is not a 60 year legacy of low-powered designs from which we can cherry-pick our favourites

The best sounding low-powered amps I have owned have been:
RAT BH5 mod: Blackheart BH5 + valve rectifier + 6L6 mixed in parallel single ended with the EL84 + new OPT. Less than 10w, combines 6L6 sound with EL84 breakup
Wienbrock ME-1. Push-pull using one 6SN7 dual triode valve, plus basic tonestack + valve rectifier. Very low power (1w?).
Biggest problem to ovecome is having no tight bottom end, and getting the right speaker.

My conclusion of buying and selling a lot of amps recently is: the reason some models are so popular and are reproduced so often is that they are the designs that, by fluke or effort, were the ones where all the many factors in the amp came together to create something really, really special. You certainly can tell when you play one.
I've felt this way playing a Matchless DC30, a DZ30, JTM45, Twin II, BM50, Wienbrock ME3 and ME4, Vox AC15H1TV, AC10 Twin.

Whilst it's a fair objective to make a lower powered version of a classic, you have to accept that you're really throwing the dice again, and 98% of the time, you won't be fortunate enough to match the sound of the classic.
Using different valves (to the usual suspects), you're back to the 50s with Leo, trying combinations out for the first time - some designs will work, some not

btw biggest range of low power amps I've seen is a EVA (English Valve Amps), they do about 20-30 models of Marshall derivatives.
I tried 3 at a show, they sounded very good, but I can't pass judgement on any amp until I've had it to myself for a few days in a quieter situation