HDTV on my iMac?

First of all, hello! This is my first post on Mac-Forums.

Right now I have the Elgato 250 Plus (link) which I use to watch TV on my computer and sometime play my PS2 on my nice 24" iMac (2008).

I've got an Xbox 360 as well and would love to be able connect it to my iMac like my PS2. I've searched and searched online but I only find links to info on how to connect your iMac to you HDTV (not what I want to do).

I thought Elgato used to make an HD version that wasn't network only, but it's no longer on their site... Any help would be greatly appreciated!