Hi peter, thanks for the reply.

I have ruled out scenario 2 - connecting two amps to the same speaker
terminal - recipe for disaster!

Scenario three could sound odd, you're right.

The first scenario would work as I can bypass the pre-amp on the
stereo amp and just use it as a power amp. I just run the receiver pre-
out's to it and have the speakers connected to this. My confusing
scenario 4 was exactly the same as this, but adding ANOTHER set of
speaker cable from the original receiver to the separate set of
crossover terminals on the same speakersl. I have found out this is
actually bi-AMPING, I think. I wonder if the tonal qualities of the
stero amp and receiver would be different though - would this have an
effect I wonder??

Sorry, I'm thinking out aloud here!