A: This is not recommended. While it can be connected to the K3S, the K3S already has the same preamp built right into the radio. Adding another preamp, generally, would only serve to raise the noise floor and add little to the initial preamp built into the K3S.
The original K3, however, will benefit from adding the PR6-10 and is recommended for that reason.
A: The PR6-10 can be added into any other radio that uses a receive-only antenna connection. Further, it has a control signal so that it can be switch in and out of the receive antenna circuit when commanded by the radio or from a separate switch system designed by the operator.
A: No, the PR6-10's case has been designed for operating inside the shack. While it can be mounted remotely, the operator would need to install a suitable weather-proof cabinet for it.