Ps3 defaults to 576p when connected through onkyo...

Question

Help Please! PS3 defaults to 576p on HDMI when connected through Onkyo 606 on HDMI to Sony 46x3500 TV

I've tried soft reset on PS3 to detect new HDMI settings, but it keeps only finding 576p! (Onkyo picks up audio formats OK though)
When PS3 is connected direct to TV and reset it finds 1080p straight off.
Sky HD is also connected through Onkyo 606 on HDMI and resolution changes to 1080i fine.
I've tried changing around port assignments and cables but same problem consistently happens.