Do you want one at a time (switch) or both at once (mixer)?
I think mixers will generally be higher quality (and more likely to have a grounding screw), and they also do switching, since you can mix one source to zero and the other to 100%.
But I’d say you probably want each to have its own preamp before switch/mix, and they have ones with grounding screws. Then it’s standard ungrounded RCA into the switch/mixer.
And at that point, if you’re using an amp with multiple inputs, you use that as the switch.