How to split a signal to inlcude subwoofer?

I think that my question is most simply stated as a 'how to' split signal issue. My setup is pretty simple. It starts at a tube pre-amp. The

pre-amp has 3 pairs of rca plugs that allow me to input 3 sources. CD player, Blue Ray connection and a direct to smart phone input. My problem

and/or question stems from the fact that I have only one output pair of l/r channels exiting the pre-amp. I have 2 power amps that I split the

signal by going through the equalizer/splitter that comes with a pair of Bose 901 speakers that I am NOT using in this setup. This seems to work

very well to solve the problem of outputting to 2 amps, and then 2 pairs of speakers, but I have a powered subwoofer that I want to add to the

system. I have tried by using a cheapo Radio Shack splitter where I have one line in then it is split into 3 lines out. 2 for the amps and one

for the powered subwoofer. It really degrees the signal and I end up with an unacceptable sound. The pre-amp does not get enough of a signal to

be heard.

I know that the Bose 901 Equalizer is not made for this application since the speakers it was made for are not being used but It seems to be

working pretty well for now for splitting the signal between the 2 amps.

Any suggestions on what I need to do to get a reasonable signal out to the subwoofer? Probably the simplest solution would be to get a different

pre-amp but I am really hoping to keep the primitive tube pre-amp that I am using now. So bottom line is I want to know if there is any way I

can continue using my current pre-amp with only 1 output out and get a decent signal to my subwoofer.

Thanks very much,
Jim Lee