if your receiver support upscale 1080P,

the your astro will be FULL HD wannabe,

at least 10-20% better than normal pic.

of course you can upscale to 1080P, i've tried w/ my former Denon 1909, it's upscaled quite nicely w/ faroudja.

most of mid-low end receiver only support upscale or upconvert using the same connection (HDMI > HDMI, or component > component) and does not support different connection ( composite > HDMI output)

feel the difference between composite and S-Video, absolutely you've got better performance.

next try upscale to 1080P, although it's not look good (since the source only 480i) but slightly better than S-video.