If you look at the specs of the two, you'll see the ISB7100 has a newer Broadcom processor vs an older Sigma. I wish I could find a spec sheet to find the speed and size of the DRAM on the CIS330, but from using both it's definitely faster.
The biggest thing you'll notice is when you plug it in. The ISB7100 boots up much faster. I think maybe in half the time. I scroll through the guide A LOT and the ISB7100 does it faster (still not perfect though). This probably why I like it a lot more. If you don't channel surf this and just pick your channel and watch then it won't make that much of a difference except when you're going through the menu or on demand.
The other issue I noticed that the longer you leave the CIS330 without rebooting it slowly gets slower and slower. The ISB7100 doesn't really do this. I'm not sure why because it seems like a software issue, but it could be that the newer hardware is better at handling Microsoft's software and hence doesn't slow up noticeably. :P I still think that can be fixed in software.
It's also thinner if that matters. lol