The HDs are a big improvement over an already good speaker (20/20s),the SEs another step yet again. I have never had ear fatigue regardless of how many hours I've listened with any Legacy speaker from Focus on up...I bi-amped my 20s and my HDs with excellent results. With the Edge NL 12.1 amp and the refinements in the HDs and the SEs, I've not found a real need to bi-amp them but they clearly could leverage such a setup even if they don't need it to sound their best.