Either way is probably fine depending on how the A/B is wired. What the dealer recommends is fine in all cases, so I would go with that to be safe. Probably not the case with your AV amp; but on a small percentage of amps the watts are cut in half per channel if you choose A and B. Just putting them all on A does not increase the load on the amp. It is no different than on a pair of regular non-biwire speakers.
Biwire speaker cables are wired internally, the same way the dealer is telling you to wire the separate pairs.
Biwire speaker cables are wired internally, the same way the dealer is telling you to wire the separate pairs.