Welcoming the excuse for a new tool, I picked up Festool’s DTS 400 REQ to reach areas where my Festool ETS 150/3 wouldn’t reach (aside: the DTS 400 REQ worked well for its intended purpose, but I agree with one reviewer who missed the symmetry of the DX 93: You go through more paper not being able to rotate a sheet on the pad). I began sanding at 60 grit and regretted I didn’t have any 40 grit (or even lower) on hand. I used the ETS 150 as much as possible, then switched over to the DTS 400 to reach into the corners of the treads and risers, working through higher grits to 180. After a weekend of sanding, I vacuumed the freshly-stripped wood and wiped it down with a damp cloth. As a probably-not-necessary step (or act of masochism), I then took a quick pass over the stairs with a card scraper. With one last vacuuming, the stairs were ready for a new top coat.