It's an interesting idea, but do you really need a box with analog stuff for that? I bet the same can be done in software and then you can make profiles for different kinds of tube amps and tweak it to your own taste.
I had a DJ500 and liked it very much indeed. I think it was beautiful also. The automatic sheet feeder was a dream after all that chain paper jams of my 9 needle matrix printer and you could actually talk while printing. The cartridges dried out way too quick though if you didn't print every day.