Up until recently, I used a Niles AXP-1 rotary switch for this exact purpose, feeding my SB2 direct to my Sunfire amp, and alternatively feeding a Yamaha RX-V1000 (pre-outs) to that same amp, for home theater playback. It sounded fine, despite the extra sets of RCA interconnects required. However, seeking to inject some "tube magic" in my system, I recently upgraded to the Modwright SWL 9.0SE pre-amp, which includes a home theater bypass loop. I ended up giving the Niles switch back to the audio friend who had lent it to me. However, they are available with a street price under $75. There are also many other (expensive) passive switches out there.