Hi there...thought I would add my two cents worth... there are tons of high quality great sounding pedals out there that I'm sure could solve your problem...ie clean and dirty at the same volume through a one channel amp...A boss overdrive or Ibanez tube screamer should give you good result...they will drive the amp into a distorted lead tone without losing too much of the tube sweetness...the thing to avoid is a distortion pedal...!!! There is a difference between overdrive and distortion and overdrive will always sound better in front of a tube amp...

But...if you cant find one you like and decide to go down the two channel amp route then you should find that there will be an independent volume control for each channel in addition to the master volume...I can't say for certain that every amp will have this but in my experience this is the case...

Hope this helps...
Craig...