The differences that I know of:
- The 622 can record three channels at one time, the HR20 can do only two
- The HR20 has two ATSC/OTA tuners, the 622 has only one
- The HR20's EPG shows info for all your local ATSC/OTA channels including an subchannls, no need to have a local channel package to get the guide info.
- On the HR20 you can connect an eSATA harddrive that replaces the internal drive on the HR20 for extra capaciy. However you loose any series links and other settings since that's stored on the harddrive and you can't copy things from one to the other.
- The HR20 has the ability to play MP3's or view JPEG's from a LAN attached PC using the approriate software on the PC.
I know the 622 has a number of features that the HR20 doesn't but since you already have a 622 I figure you know what those are already.