Worth it for the sound alone. Don't have an HDTV, but playing in 5.1 is worth the extra money. Haven't done the side by each compare of RCA vs Component though-if anyone would like to provide pics though...
I have the Advanced AV Pack and am running DD5.1 and component progressive into my 51" Pioneer Elite RPTV. I haven't specifically compared it to RCA composite and don't really need to as I know it will blow it away. Even with my Playstation 1, switching from composite to s-video on my RPTV was a big improvement. So at the very least, you will want to be running s-video with your XBox, and if you have the capability go with component.
Just to clear up any confusion. The advanced AV pack has S-video and composite, but not component. It also has the optical connection for 5.1, which as someone else mentioned is worth it alone. As to whether you see a big difference between S-video and composite will depend on your monitor, but it shouldn't be worse. The High-def pack has component output with 5.1 output.
Eric,
Monster also makes comparable sets for high def. I am using that one right now for my HDTV and it works fine, although some have reported problems with the 5.1 output. In fact, the one thing I don't like about it is that the Monster version requires a special adapter for the optical output, which as far as I can tell can only be purchased with their optional optical digital cable. The microsoft kits allow you to use any optical cable. They sure look purrty though and are extra long.
Agreed with above - if your monitor supports it at least get the Advanced HD Pack for S-video. I believe there are other 3rd party providers besides Monster if you want to keep your options open. And the 5.1 audio is a must if your system can accommodate it. Fantastic.
I just want to warn people off from mad catz's ultra a/v kit. This unit provides s-video and optical outputs. But I was unable to output dolby digital from the optical output. The unit fails to provide the necessary menus from the dashboard to engage dolby digital and dts.
Honestly, I'd steer away from ANY 3rd party Xbox stuff right now. There's not a big price difference (I got the HD pack for $30 CDN-I think the MadCatz one was 25), and the MS stuff seems to be of much better quality. A friend of mine got burned with one of the Interact controllers (piece of garbage) as well as a cheap memory card.
The first thing I picked up when I got my X-Box was the Advanced AV kit.....the 5.1 sound was one of the big factors involved in my decision to trade my PS2 for an X-Box. As for 3rd party stuff, Interact seems to have really gone downhill quality-wise over the last few years. I bought one of their controllers for my PSOne recently, and it was a total piece of garbage.