Remove the speaker seating from the top of your speaker stand. Most models will pull straight off, but some may screw off, or require pressing a catch release or pulling a pin. What you should have left is an aluminum pipe that may be anywhere between 1 and 1 1/2 inches in diameter.
Find a metal (brass or aluminum are best) pipe end cap that fits around the outside of this pipe (generally 1- to 1/2-inch inner diameter). It's okay if it has a little bit of space around the edges.
Place the cap in the bench area of your drill press, inside a vice to hold it steady. The cap should be upside-down so the drill is going into the cap from the underside.
Insert a 1/2-inch bit into your drill chuck and drill a hole in the center of the cap.
Remove the cap from the vice and turn it sideways. Clamp it into the vice again and change to a 1/4-inch bit. Drill three 1/4-inch holes around the outside of the cap, evenly spaced around the circumference.
File off any sharp edges from the drilling.
Place a bolt through the bolt hole in your can light's yoke, with the bolt's head toward the light. Thread the bolt through the hole on top of your cap, so the hollow portion of the cap is away from the light, and then tighten the nut onto the bolt with a socket wrench.
Place the cap onto your speaker stand pipe's upper end and thread three 1/4-inch bolts through the three holes around the outside. Tighten them down with a wrench until they hold the light snugly, but do not overtighten or you will dent the speaker stand.