We need to be very clear about this ...
... or no difference at all?
It's most likely that they're identical between ACR and PS when both are viewed at 100%. But I need you to confirm that before we move on to the next part of the discussion.
Thanks. Now could you zoom in to 100% on the file in ACR, and take a screenshot to show me how it differs there?
This is only half of the recommended minimum RAM for CS6. You're likely to have problems.
First things first, please don't halve your hard drive space and computer power by working in 16-bit. It's completely unnecessary.
Secondly, please show me a 100% crop of the grain in Photoshop.
Thirdly, fill this out for me.
No, it's ok, let's just talk it through. My first question is - do you think you'll need to extend the flooring either side also? Or can you crop it close enough to prevent that necessity?
Try adding a Levels layer, and move the middle slider on each of the three channels:
Red channel 2.50
Green channel 1.50
Blue channel 1.35
Then invert the mask and paint on gently where needed.