Your current dish actually has an 8-output multiswitch. Your new dish will be similar .... 4 lines coming from the new dish to a new 4-input multiswitch (Zinwell WB68), with 8-outputs for your various Receivers and DVRs.
The extra LNBs enable reception of DirecTV's new Ka-band satelliltes at 99-deg W and 103-deg W, along with the existing satellites at 101, 110 and 119-deg W. These new satellites deliver local HDTV channels to selected cities using a new MPEG4 compression, and eventually additional HDTV channels.
Sony SAT-T60 120GB (v3.5b)
HR20-700, HR20-100, HR21-200 HD DVR
HR10-250 HD DVR 400GB (v6.4a)
H21-200 HD Receiver
R10 DVR 160GB (v6.4a)