I have this setup and it works. I use a Mac mini with the Elgato EyeTV HD. The EyeTV uses a component input so you can get 720P. In my system I use an HDMI splitter from my Scientific Atlanta box. One of the HDMI leads goes to an HDMI-Component converter and that to the EyeTV. You run EveTV on the Mac and can record while the cable box plays the image. The nice thing about EyeTV's software is you can then edit out the commercials and export the file as a MP4 video.
That's about all the good news with the eyeTV. The IR blaster (to change the cable box channels) has never worked and the files inside the EyeTV repository have an .eyetv extension and you can't edit them outside of it (or at least I don't know how). You can't import files into EyeTV either if you want to do more editing.
Further I can't get the EyeTV learner to work with my Cable controller. To get it to work you have to buy a software package called iRed2 which will correctly send ir signals to the cable box.
In summary, it works...barely. If you HAVE to copy from your DVR get it. Just don't believe anything else they say about its capability. Tech support is abominable; you have to jump through all sorts of procedural hoops and in the end you're lucky to get your problem solved.
Thanks, Rich