Ok. My opinion differs a little. I think the M10x/C10X smokes the 509X. I was never impressed with the Luxman integrateds. I had the 509AXII and it was a failed experiment, unfortunately!
I'm not sure why the Luxman has received lukewarm praise. I would go for the C10X. You would have a 'state-of-the-art' system for many years to come. I wish I had gone in that direction, but my wife loves the blue meters.
Best and good luck!