Hi M James: 'Pine Box' stairs? Does this mean your stairs are a series of pine boxes stacked on each other...?
(smile). Nahhh....just funin......:-)
There are a couple of ways you can convert your pine (or doug fir) treads and risers to a hardwood finish. One is to replace your old T&R's with the hardwood variety....most of which these days are MDF with a hardwood veneer. Another way is to buy (or resaw yourself) 1/4" X3" (or so) hardwood slats that you can then adhere to your old pine T&R's, applying a solid hardwood ripping to the leading edge of each tread and routing it for your bull-nose. This option may cost less, but is quite a bit of work. The final way is to simply remove each T&R and sand and refinish. You'd be surprised at how nice they will look.