Hi Mark,
Welcome to AudioCircle. As I type this I am listening to the Superfly soundtrack on my WT Amadeus.
As you likely know from your research, the difference in the two models is just one of plinth material. This is in contrast to the Simplex (not yet available in the US), which is a different design in a number of ways. I have not heard both side by side, and opinions tend to differ about whether there is an audible improvement in the GT. IIRC, some say that the Amadeus is a 30% improvement over the Simplex and the GT is another 30% over the regular Amadeus. Given the substantial similarities between the WTA and GT, I am a bit skeptical that the GT is that much of an improvement, if any, sonically.
Hopefully folks who live near a dealer who could listen to both side-by-side can chime in.