I own the Herron and have owned the Rhea at the same time. I saw what I thought was a good deal and bought the Rhea out of curiosity. It took while to figure what tubes to put in it to get it to be transparent which it wasnt with stock tubes. I found that the 6DJ8 was the key tube to obtain the voicing I was looking for with a Telefunken being the preferred tube. For the other tubes (v1-v4), I found two different combinations that worked well. The first is all Telefunken and the second is vintage EIs in v1&v2 with GE black plate 5751s in v3& v4. I liked what I heard enough to buy an Aesthetix IO. I sold off the Rhea once I had the IO but regret doing so. The Herron sits idle these days.