The Tried & True Oil finishes Till E. recommended gave a great look to the birch ply. It really brought out the grain and gave them a nice amber glow. I didn't use any stain, just the oil finishes.

Wayne, how high does the wall have to be to use the Pi 7's? I have an area in my basement that has a granite wall on one side about 7 feet tall, and on the other side there's a brick wall that's about 3 feet high. I could finish it off into a room, but then both of the new corners would have a stud/drywall, and the brick wall would have drywall above 3 feet. I'd also have to put a door in which would be close the speakers. Any chance?

I suggest you take existing speakers and point them into the corners. For this listening test, the tweeters will be pointed in the wrong direction, so don't let that fool you. Listen primarily to the bass and midbass, and listen for the quality and uniformity of response. If you like what you hear, then the corner is satisfactory and you can start cutting wood!

Wayne