There's no benefit in connecting your Sky HD to the onkyo 507 via HDMI anyway(other than for video switching) ,as it doesn't upscale and Sky HD cant output DD 5.1 over HDMI.
So if you've got enough HDMI input's on your TV,i'd by-pass the receiver and just connect SkyHD directly to the TV with HDMI and to the receiver with optical for surround sound.