Im using a diamond 300N antenna, so I bought a N to F adapter for the antenna. Everything seemed to go together ok, are you saying those don't work? Also with the PPC PNC, have you used one? Do you have the VT-HE compression tool?50 ohm and 75 ohm BNC connectors are physically compatible with each other, so no issue using the PPC 75 ohm BNC compression connector on the RG6, then going directly into the SDS200. And no, the impedance mismatch doesn't much matter for RX only application, so don't worry about that either.
Just don't try to mix and match 50 ohm and 75 ohm N connectors, as they use different diameter center pins, and you'll either not have full contact between connections (75 ohm pin into 50 ohm socket) or you'll risk damaging the female center socket (50 ohm pin into 75 ohm socket).