removing stain from Californian redwood / Red pine

hi there. we are renovating a 100 YO house which has nice original Californian Redwood skirts and architraves. They were caked with paint. We decided against removal and dipping because the plaster is a bit on the brittle side and it would most likely have created another mess (in hindsight the mess & replastering would have been worth it ). but anyway, we have stripped the timber using a heat gun, some chemical stripping, and then a lot of scrubbing with metho and coarse steel wool.
What we are left with is a nice finish, but quite different colours in the timber. ie.. very dark around the front entrance, and the hallway skirts & doorways are pretty light. I think this is because we have not removed the old stain from the timber, and some areas may have been more heavily stained than others.
Sanding works, but is very hard going and the paper clogs quickly. It also looks patchy if we don't sand back the entire area to the same level. So, 2 questions :

1. is there an attachment which can be used on a drill or grinder which can remove the surface stain reasonably gently ?
2. is Oxalic acid suitable for removing the deep stain colour, or is there another alternative?

any advice would be much appreciated.
thanks,
Cameron.

Deep stain?
The aged timber is a very dark red, are you confusing the natural timber colour with a stain?

no, I dont think I am, because we have sanded back a couple of areas to a very rich raw red colour. but the unsanded area, expecially around the entrance is almost a purply chocolate. if I sand it, it comes back to the raw reddish colour.