Two boxes... what do I fill them with?

[schmalex]

I have two 1cuft/28lt. sealed enclosures. What should I do with them? The baffle is 11 1/4"/28cm.

The very first loudspeakers I ever bought were a pair of Boston Acoustics HD7s. They have served me well over the years. My roommate in college blew the tweeter on one side, but that was easily replaced. Nearly 20 years later, I noticed that the foam is torn on both of the woofers. I could re-do the foam, but I would just rather use these as a project box to try out new stuff. The boxes look pretty good, and are of decent, not great quality.

I've never owned full-range speaker, so why not give it a shot. Any suggestions? Budget would be no more than $70.