Receiver Dilemma

Want to connect my vintage Pioneer SX-650 and my modern 919AH-K to one set
of Paradigm Mini's, is their a way to do this? I don't want to potentially ruin any of the units.
Went to an electronic parts store, reputable in my town, and the guy advised not to do this, because (as I remember) problems with the electrical current. He suggested connecting the 650 to the 919 by way of Tape Out to Aux in, which I did and now the 650 and my vinyl are back to the neutral/lack of warmth sound of my budget AT phono stage :(

Can't I do some kind of switching box or something?

Any help welcome.

http://www.nilesaudio.com/product.ph...rdcdID=FG00003