zExporting to Sxs card from FCPX

No idea how to export, sorry share, an edit back to an SxS card. I can do it from fcp7 via content browser (on the same rMBP) but no info anywhere, that I can find about doing the same from fcpx.

I'm using fcp x 10.2 (trial) with Sonnet thunderbolt Sxs reader. Currently reduced to exporting a master file from Fcpx importing into fcp 7 and writing to card from there ...
Read somewhere that the should be an option from within fcpx in the master file settings, can't see anything.
Any help much appreciated.