I currently own the Genz-Benz Streamliner 900 head, and I'm very satisfied with it. But I noticed that the Genz-Benz Shuttle 9.0 is fairly similar to the STM 900 in many aspects. Both are 900 watts at 4 ohms, and both have roughly the same front controls (with the exception of the Shuttle having the additional three signal shape controls). I also understand that the STM has three tubes in the preamp, whereas the Shuttle has one. The STM is only around $130 more than the Shuttle brand new. So my question to those of you who have played both, is how do the two differ in tone? Please list any other differences you've noticed between the two heads, as well as any pros and cons of both. Also, if you had to choose between the two heads, which one would you take? Thank you for your time and input.