Commonly available source switchers are analog affairs, which means that you’d need to insert DACs into the signal chain and immediately lose any potential improvement over the BeoSound Core’s internal DAC from the AirPort Express.
If you were connecting a turntable and a CD player you’d have an easier time of it.
Now that being said, you’re not going to beat the DAC in the BeoSound Core as far as I’m concerned. I’ve connected my BeoLab 20s to an NAD M10 and a Naim Uniti Atom and the Core whooped them both handily using AirPlay 2 as one of the test inputs.
I’d connect your TV and enjoy the AirPlay 2 natively.
