I sent my 9.0X back to Dan for both the T upgrade and his umbilical, and it was a major improvement. Sweeter top end, fleshier midrange, and no loss or flabbiness of bass. The T power supply has a hole in the cover so you can roll any 5AR4 family rectifier, including ones in the ST bottles.
If you're planning on keeping the 9.0X, the upgrade is worth every penny.