A DirecTiVo can record 2 programs on 2 different channels AND let you watch a third recorded show at the same time. A SA TiVo can record only one show while letting you watch an already recorded one.
The DirecTiVo has no quality settings because it records the actual bitstream as it comes in from Directv. There is no loss of quality on the recordings - they look EXACTLY as good as the live signal. A Directv receiver/SA TiVo setup has to decompress the signal then compress it back down using the SA TiVo's own (inferior) encoding chip. Even leaving the TiVo set at "Best" will not equal the DirecTiVo's PQ.
The DirecTiVo CANNOT record anything except Directv's signal, so if you don't subscribe to locals from Directv it won't record them from an OTA antenna - it will only pass them thru to the TV without recording. A SA TiVo can record from any input source.
The DirecTiVo can record & playback a DD5.1 soundtrack if the program has it. A SA TiVo cannot - it has no DD5.1 input or output.
The DirecTiVo gets its guide info from a constant trickling stream in the Directv signal and only has to dial out once a month to verify service with TiVo. The SA gets guide info either from daily calls (no more 800# service, so long-distance calls may be required) OR from a TiVo service paid program shown on the Discovery channel late at night.
Did I mention recording 2 shows at once ?

This really is the killer app - it makes conflict resolution a snap. I never watch live TV or commercials any more because my DirecTiVos have so much stuff recorded that I can choose from. I don't even know when many shows are scheduled on live TV - I watch when I get ready
