Bblilikoi -- Based on your numbers, I think either of the contemplated hookups should be OK. The CL-15's 50 ohm output would normally be looking at a single 100,000 input on the PrimaLuna. This is a high ratio of 2000-to-1, quite satisfactory. If you double the number of inputs used on the PrimaLuna, you are doubling the current required from the CL-15, or cutting in half the impedance presented to the CL-15 by the PrimaLuna. The result would be equivalent to a still-quite-high 1000-to-1 ratio. Should be fine.
The Electrocompaniet may have had a sensor relay that chose the XLR input, shutting down the RCA. It sounds like both the XLR and RCA were plugged in to the same input source selection (e.g., "Source #3," which would have both XLR and RCA sockets), in which case the preamp would be forced to choose one and mute the other. To avoid this in the future, try using different input source selections if possible (e.g., "Source #3" for XLR and "Source #4" for RCA). Good luck.
The Electrocompaniet may have had a sensor relay that chose the XLR input, shutting down the RCA. It sounds like both the XLR and RCA were plugged in to the same input source selection (e.g., "Source #3," which would have both XLR and RCA sockets), in which case the preamp would be forced to choose one and mute the other. To avoid this in the future, try using different input source selections if possible (e.g., "Source #3" for XLR and "Source #4" for RCA). Good luck.