The preamp is housed in a unit designed for outdoor exposure. It will provide the best results if located near the antenna. Also included with the preamp is a separate power supply, which is intended for mounting in a protected (normally indoors) area with access to an outlet. The power is coupled into the coax to be sent up to the outdoor unit.
As I mentioned earlier, the ANT-800 has a functionally similar arrangement. If you retain the ANT-800 for the time being, you'll not be able to power the ANT-800 and the new preamp via the same coax down lead. The two antennas need separate down-leads and grounding blocks.
Once the signal from each antenna is output from their respective power insertion devises, they can be combined using a UHF/VHF signal joiner. The output of the UVSJ can then be cabled a single coax run to the TV.
Radio Shack #15-2586,
http://www.solidsignal.com/pview.asp?p=uvsj and
http://www.amazon.com/Antennas-Direc.../dp/B008PBTPN4 are examples of passive UHF/VHF combiners.