The SS Carmen has a lowish output of just over 2mV. The Decware prefers 5mV.
You could check with them to see if you could swap the 12AU7 for a 12AX7 for more gain which might give you some more "authority."
You could check with them to see if you could swap the 12AU7 for a 12AX7 for more gain which might give you some more "authority."