There is a thread on this subject called ' Soto de Luina to Cavedeo disused alternative' last post 15th Apr, I would give a link but my mobile is not up to it.
The hospitelero at Soto de Luina advises pilgrims not to walk this way, the main reasons that the route is overgrown in parts, the way marking is patchy, and its not a good place to be if bad weather comes along. I followed his advice and went the asphalt way, its quite straightforward, mostly asphalt, shops every now and then. Three pilgrims took the other way by mistake, said it was very hard but just about the most beautiful section they had walked. Saw another blog on here two years ago a couple of English pilgrims went that way, had a very challenging day but said that the scenery and trails made it their best day yet.
Both ways are historical routes, the mountain one is neglected, its called Serra de las Palancas.
Good luck.