My Avant is capable of playing movies in DTS. 

Am I correct in thinking that a DVD with DTS sound plays rear sound effects in both the rear left & right speakers (mono)?

and playing a DVD with DTS-ES would not make any difference?

Yes, there are discreet surround sound channels, each being fed with separate information.

The BeoSystem 3 can decode DTS-ES I believe.

So DTS plays 5 separate speakers (+subwoofer) individually, and so does Dolby Digital?

But Pro-Logic plays only front left, center, front right and rear (no rear split)?

DTS-ES needs an extra rear center speaker and would need a BeoSystem 3 anyway?

A DTS-ES DVD would sound no different with my set-up? ;/p>

BRiTOPS:

So DTS plays 5 separate speakers (+subwoofer) individually, and so does Dolby Digital?

But Pro-Logic plays only front left, center, front right and rear (no rear split)?

DTS-ES needs an extra rear center speaker and would need a BeoSystem 3 anyway?

A DTS-ES DVD would sound no different with my set-up? ;/p>

Correct!