The reason some of those sites suggest that you might need to replace the wood in the end, is because someone, somewhere, probably tried everything under the sun. And if the collecive minds on another site, full of folks that know what they are talking about, say that if the tanins are stained there is nothing you can do, then why not go with that?
Add up all the products you bought, the time involved using them, the sanding, going to forums, etc., and you probably could of bought an entire new floor at this point.
I think at some point, you will cut your losses and replace the damaged wood. That is my advice also.