Hi FlamingHedgehog, adding a T will create losses and you’d be better off putting them to to separate antenna ports. That way you can switch between the two for comparison purposes. The RSPdx can only see one antenna at a time (unlike the RSPduo which can process both signals at the same time with its independent tuners).
There are some good Facebook groups dedicated to loop antennas, if yous search for “Mag loop” or similar.
Best regards, Jon