Quite simply, large backcountry browns in spooky water don't always require a subtle approach: in fact, this will more often than not result in them swimming hastily for cover as they sense the slightest imperfection in your dry or nymph presentation.
No, you need to get right in their face. Forget specific feeding, give them something they want to attack.
Brian Read and I had one such fish that beat us many times despite throwing our 'A Game' nymph presentations over a number of weeks. Tricky water and a large, wily fish foiled us every time.
A few modifications on the cone-head marabou streamer I grew up fishing resulted in a much more durable, full of movement item-to-be-preyed-upon and the next morning back at our pool, a 12.5lb high country brown posed neatly for a photo with a very deserving angler.