No need to buy another splitter... the splitter built into the CM-3412, 3414 & 3418 are no improvement over the existing passive splitter you already have. The amplifier is the same in each of those models as that used in the 3410.
The CM-3410 can be powered via the coax... that allows you to mount the amplifier close to the antenna even when there is no outlet close by.
If you are willing to run a new piece of coax from the outlet to the amplifier, you won't need the PCT MPI-1G Remote Power Inserter. The connection between the amplifier and the power supply 'brick' is regular RG-6 coax terminated with standard F connectors... Just like the rest of your cables.
The PCT MPI-1G Remote Power Inserter comes in handy when you want to avoid running coax from an outlet to the amplifier. You'll still need a short piece of coax from the power supply - into the PCT MPI-1G Remote Power Inserter.
It boils down to which option makes sense in your situation.
Here's links to the instruction sheets:
http://www.pctstore.com/v/vspfiles/a...on%20sheet.pdf
http://support.channelmaster.com/att...tion+Sheet.pdf