I would suggest you get the Y-connectors at Radio Shack and see if they work for you. If the input impedance of the SS amp (even when off) is much lower than that of the tube amp, it will shunt most of the signal and you will get little out of the latter.
If it works, then you can consider investing in higher quality connectors.
Kal
If it works, then you can consider investing in higher quality connectors.
Kal