if you use MC 26 on a Mac, then you can use many different ways to connect to your LS50. If you use just "wireless", then probably you mean you connect your Mac via "AirPlay" to the LS50. In that case the LS50 do not appear in MC 26 as an audio device unless you select it on the Mac as you current AirPlay device. Once selected ("system setting >> sound" select 'LS50 AirPlay') it appears also in MC26 ("Tools >> Option >> Audio", look for AirPlay). But I do not use this connection with my KEF LSX speakers, because Apples AirPlay can only play up to 16Bit/44,1kHz, thus you don't use all the capabilities of your LS50.
You better connect to your LS50 via DLNA (for this you must activate the MC 26 server (Tools >> Option >> media network >> library server for DLN devices). The only disadvantage then is, that you can't use CloudPlay, since CloudPlay does not work (currently) over DLNA.
The other option would be to use your optical or analog audio output of your Mac and connect it to your LS50 (but unfortunately with a cable and probably and additional DAC).
Achim