I've done it! A relative of mine had two Gallien-Krueger 250ML guitar amplifiers, which are an interesting bit of kit, but the 5" speakers had foam surrounds that rotted out. I ordered and installed generic replacements from Parts Express. For my part, I was just curious about how the amps would sound.

As for the Bose, they were nothing special as speakers, and I already had a stereo that I was happy with, so I disposed of them.