You're going to be good. I measured the terminations on both my Reactio and Reactio Plus models using gauge pins, and they are both 2.1mm ID's.Agh! - Just seen the latest post by JEB42, while I was typing!
I think I'll just wait until Thursday, when the JS-2 and cable is due to arrive. The Uptone Sapphire cable is terminated 2.5mm at the LPSU end and I have requested 2.1mm at the Seismion end (as a result of information posted above).
I'll try it plugged in both ways and that should settle things! I can always return it and order the 2.5mm termination at the Seismion end of the cable!
I'll keep everyone updated!