I have been looking into buying a Samsung SRD 1673d and from there web site.....SRD-1673D The next generation of Samsung’s DVR products add Full HD 1080p HDMI video out, support for 650TV lines analog cameras 
  
So the with this DVR as far as I can tell you do not gain anything with cameras that have over 650TVL 
  
One thing I have been trying to find out on the 1673d and the 1680d is if you can use the alarm inputs on these 2 DVR's  to turn on more then one camera at a time.....   like say I want to have Alarm input 1 to start recording on cameras 1,4,7,8 and 13  and then have Alarm input 2 turn on another set of cameras that may overlap some of the same cameras, can that be done in the software? or is it only one camera per alarm input?