Orange have made this fancy bit of ABY switching kit available at the NAMM 2016 show, it's an active pedal with 2 outputs.
There is an isolating transformer on one output which is great for keeping your amps groundings playing nicely together, the transformer is completely transparent. Both outputs are buffered too and this thing makes hardly any noise at all.
This is a totally silent ABY switcher available today, producing little to no noise or thumps when switching between amps. There's a lovely extra feature in the polarity switch which can allow you to address and phase issues bothering you. The LED light has 3 colours indication on amp, the other or both.