[Sephiroth]

The Homeplugs are attached to a specific port of the SH. If the PS3 then behaves OK, there's no association with any other part of the SH router section.

You've said that it's wireless that suffers -and 2.4GHz at that. I can't see a way that one wireless mode could be affected by an Ethernet only Homeplug. I even hesitate in suggesting you attach the PS3 directly to the SH and report what happens!