Have you ever used a separate speaker selector unit to audition speakers? Would you?

I would be more concerned about placement than switching. I recently tried my old speakers again after setting up new ones for the last several weeks to try out. The new ones ended up set a littler wider with less toe in but about the same distance from the wall so I thought maybe I could sneak the old ones just inside of them and it would be about the way they were. Either I was wearing rose colored earplugs when thinking back to how they old speakers sounded or the placement was more of an issue than waiting 5 minutes and crawling around on the floor to change the cables over. To position them correctly I would need to move the new speakers, but since this was just supposed to be a quick check to remind myself of some of the differences it wasn't worth the effort to me.

I think I'm cured of trying to setup 2 sets of speakers at a time to compare them. The potential damage to amps or switchbox noise is really secondary.  

+1 re. @b_limo  and @cat_doorman 's point on speaker placement.

@david_ten and @catdoorman - I was thinking I'd just pop one set off the stands, put them on the floor, and put set #2 on the stands in their place. Exact same placement for the comparison. Perhaps different speakers need different placements -- granted. In that case, I'd have a second set of stands ready to go.

@hilde45 That’s the point catdoorman and b_limo were making.

First, you will need to find the ’workable’ / ’close to best’ placement for each speaker and evaluate each in the specific positions each sound ’best’ to you.

Second, ideally, the speakers not being evaluated should be moved out of the space so the physical presence is not a factor (for the non-active speaker).

You will also likely have your ’original’ speakers set up to your preferences and optimized via component / cabling etc. synergies based on your choices. That may not transfer over to the second and third, and.. speaker being evaluated.

Listening positions may also need to be adjusted / changed.

There is more...

It gets tricky. : )