4 DVRs would be 8 tuners so you should be fine, do you have any more equipment though? Remember you have a max of 8 tuners per side of the SWiM16. If it just doesn't let you record two things just repeat sat setup and be sure to chose dual tuners. But if when trying to record two things or record/change channels it's giving you 771B or SFSS you'll need to move it off that side of the SWiM.