Re: How low can an attenuator go before ruining tone?
My own solution to the problem is an expensive OD pedal, the Klon. Nothing I've tried really does it like that unit. It sounds so natural on any amp it's in front of, that I can turn down the amp, and rely on the pedal to get the goods.
As far as the Valvetronix line, try and locate an AD60VTH head for around $400, and use it with your nice cab. Compared to what you heard in the store, the head on your Edana's Vin 30/H30 cab will be far better.
I just look at the amp models as overall tone shapers, then let all the good tones come from tweaking all the volumes and gains on the amp. For instance, you might find a better highgain tone using some of the cleaner models, but dialing them really gainy with all the available OD options.
Another thing you could consider is using a Vox modeling floorboard in front of your Edana, and tweak it till it sounds as natural as possible. By owning the floorboard or Tonelab, you'll also have something you can take with you when you travel.