+2 @ghdprentice
I basically no longer do A/B tests. I prefer to listen for long enough to something that I have a good sense of its sound. Then listen to the other thing. If changes are not obvious with that type of listening, I am no longer convinced they are all that important.
Regarding the use of any type of switching device, I would not want to assume that it has no effect on the cartridge loading. I think you want to go straight from tonearm to phono stage.