I don't know about compared to the S3 since I don't have one, but it tunes QAM just fine. I'm waiting for my cablecard install, but I had it scan the channels and it found a ton of them. Most are bogus or encrypted, but the main ones like NBC, ABC, etc. come in just fine. Problem is there's no way for me to tell Tivo that 3-1 is NBC HD, so no guide data. It seems to tune the QAM channel relatively quickly. I don't get the sense that it can tell the difference from an encrypted/non-encrypted QAM given the number of bogus channels it found.