Genies only works in a SWM only system. Press the dash button on your remote to find out if you have a SWM system currently installed. If you don't, you will need DirecTV to come and install it for you as you may need a new SWM LNB or SWM multiswitch.
Also we need to know whatnot her receivers do you currently have.
And FYI, the Genie can record up to 5 shows at the same time, not 6
Also be VERY careful about "buying" a used/previously activated Genie on eBay or Craigslist or similar. Get the receiver ID number (RID) from the unit and call DirecTV Access Card Department and verify the unit can be activated if you obtain it BEFORE you pay anything for it. Also know you will have to buy a new access card (cost $20) from DirecTV.
There are vendors on eBay that "sell" new equipment, and it is okay to "buy" that, but understand that you are not buying it, you are leasing it from DirecTV. You can normally get as good or better a deal by ordering it directly from DirecTV.