Oh yeah it has a stacked tube in it which is 2 12AX7's in one casing
I've searched around and can't find anything about the tube in the sxg2000 but i did find a guy that talked about sending his to a guy in VA to fix his lcd and said he changed the tube to a Sovtek and he was impressed... so I could be wrong about this but I seam to remember that from somewhere?!?!?!?!
this is what ART Says on there site in the discontinued section:
Programmable Preamps. When designing the 2000 Express, our engineers researched and designed a tube preamp circuit that rivals the most classic of vintage tube amps. The result is a sound that is warm, yet brilliant, and breathes the way only a tube amp can. The SGX 2000 Express offers 8 variations of the Tube and the Solid State circuits that have their own unique sound. Choose Tube only or Solid State only, and for maximum gain, run through both preamps by selecting a stacked option. Tone, gain and output are all adjustable. A Tube Contour control, located on the front panel, adjusts the tube's tonal characteristics. There's no need to use a speaker simulator or any other "special" black box when running the SGX directly into a console. The preamp design is so precise you'll swear the guitar is mic'd.
Which now makes me want to try some a hot "Grove Tube" brand tube. btw what do you guys think about grove tubes compared to all others?