Using Y-adapter to duplicate preamplifier outputs

It is really a question of impedance.

In theory a preamp has a low output impedance and likes to see a high input impedance (10k ohms or more).

If you use a Y adaptor you can halve the input impedance of the power amp as the preamp sees the two power amps' impedance in parallel.

Reduced input impedance on power amps can manifest as reduced high-frequency clarity and a loss of dynamics. Using interconnects with the minimum capacitance can help to mitigate this effect. Something like the Chris Venhaus DIY interconnects with eichmann bullets would probably be the minimum capacitance.

The best thing to do would be to get a relatively inexpensive Y adaptor and try it, and if it sounds OK get a more expensive one made up. I certainly would not have the preamp modified to add extra outputs, since these most likely are simply extra jacks wired to the existing output and do nothing to solve the impedance problem, but could reduce the resale value of your preamp.

Tara Labs and AudioQuest both have hard-y addaptors that work well and are not expensive.

Audioquest will also make up a y cable. Two lengths of IC, joined at one end to a common RCA and of course 2 RCAs at the other ends. .

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

Kal's advice is excellent.