Many receivers accept 1080i inputs on component, but do not allow 1080p to be converted to their HDMI output. My pioneer receiver was the same way- until I switched to all HDMI I had to set the xbox output to 1080i via component.
On the Abt website for your receiver I found:
"6 HD Inputs
Get versatile HD connection options with six HD inputs. Four HDMI™ inputs (up to 1080/24p capable) let you connect a Sony® PlayStation® 3 entertainment system, Blu-ray Disc™ player, and any 2 other HDMI-capable devices, for high definition video and audio.6 Two component inputs (1080/60i capable) provide added HD-capable connectivity and versatility. "