I have a Koetsu Black. It was in my system when I (briefly) owned a pair of Harbeth SHL-5 30th Anniversary Edition. As good as the Koetsu Black is, and it's really good, it didn't help with those Harbeths. I found them kind of boring no matter the source. To me, they made everything sound the same. Perhaps my room wasn't a good fit. All I know is that they didn't work out for me.