I've run out of line inputs on my amp and would like to connect an additional line-level source. On the understanding that there would be no occasion when the two source units would be powered up at the same time, could I just use a Y-connector or would I be obliged to use a switch box? I'm wondering whether the passive presence of the switched-off unit in the circuit might affect the overall result, or whether the line-of-least-resistance process applies.