What is the basic difference(s) b/w the QIP 6416 DVR and the QIP 7216 DVR?
From a users standpoint there is only 1 real difference. The 7216 has an RF (NTSC) output and the 6416 doesn't. Both have a 160G hard drive (the 16 at the end of the part number indicates the hard drive size in GB dived by 10), support full VOD, Widgets, and have a maximum output resolution of 1080i. Netiher has the USB, external video, or Ethernet enabled. There seems to be a higher incidence of HDMI problems with the 7216, but this has been minimized with the latest firmware update (IMG version 1.7.1).
On the technical side the 7216 has more memory for the processor, a newer processor and supports MPEG-4.
Hope that answers your question.