I am assuming that your LNBF's are dual's (2 outputs each)
Are you keeping the 4000 as an active receiver ?.
If not then it's pretty easy, get another SW 21, run 2 more outputs from each LNBF to the new SW 21, and then run that output and the current one to the back of the 721.
If you are keeping the 4000, then you must upgrade your 2 LNBFS to a Quad (four outputs, each with both 110 and 119 on them), run two new lines to the 721, and hookup your existing line to the 4000 to the 3rd out of the Quad. This is by far the neatest setup. Dish Depot has a pretty good deal 721 with Quad for $650, and then you can ship them your two LNBF's and SW 21, for a credit, might turn out that it doesn't cost you too much for the Quad which is usually $150
Lastly you could keep your 2 LNBF's and get a SW 44 switch. But I really don't know the advantage of this over a Quad, since a Quad is neater (no switches) and easier to setup. I think prices are very close the Quad being a little more I think.
Lastly if your LNBF's are not dual outputs, then just get a Quad.
Hope that helps
Bill
