Any speaker that you wouldn't cry over if it got damaged basically. You could even go to GoodWill and buy a pair for $5. Similar resistance doesn't matter. What you're looking for is the signal clipping point, and then not exceeding that volume position on the Lyr (staying well below it actually, since audible clipping is severe to minor clipping). Power isn't an issue here since you have plenty of it.
Edited by brunk - 2/5/14 at 2:25pm