No reason it wouldn't work with a regular stainless steel cable.
Make sure the cable/outer routing is smooth as per Orange's specs and it curves nicely around to the rear mech – not too sharp a bend nor too long. Check the outer is seated into the ferrules properly and, if needed, file or grind the ends of the outers square.
I'd bet that it's possible the mech hanger isn't aligned properly but you need an alignment tool to check that – you can't really do it by eye.
As suggested, read up on the Park Tools site or on Sheldon Brown. Set the highs and lows with the chain off and do the "b" screw adjustment properly too.
Good luck 🙂