OK, McDuck: I challenge you to tell us how the scheme pictured below could possibly have a problem due to having two speakers in series (this assumes the amplifier is happy with an 8-ohm load):
**broken link removed**
(This is actually currently relevant to me, as I'm advising a friend who's installing 8 speakers in the ceiling of a hall. I gave him a wiring diagram to show how to wire the speakers in series/parallel to get a 4-ohm total impedance out of the 8-ohm speakers.)
Now, granted, it all depends on factors such as whether the speakers are in the same enclosure or not, what kind of acoustic coupling exists between them, etc. Such things may make all the difference in the world to audiophools (meaning the types who actually buy gold-plated connectors and such). But to the rest of us, where these speakers can all be considered to be independent drivers, it matters not.
I look forward to your explanation.