In most cases it does not matter at all . But if the amp that sounds the very best has a very sensitive speaker protection circuit then it can be an issue .Apparently they even out the very odd impedance / frequency variations of the ESL57.
Not quite sure why this matters with a decent amp though.
I think I have a pair , Will have a look and report back.I thought i had this sorted but would appear not so still looking . Reason for asking for used is I would prefer to reuse/recycle if possible and many of us myself included have things in boxes drawers etc we are not using . if anyone has a set let me know .