I've had a really great experience using my Schiit Saga Preamp with my Adcom 5800 power amp (Nelson Pass design 250 watts/channel into 8 ohms, and over 400 watts/channel into 4 ohms) I bought another Saga Preamp and will be using that one with my Acurus a250 power amp soon. I also prefer the Russian Tung Sol 6SN7 vacuum tube. For my headphone amp, I use the Creek OBH-11. I have 3 units, one new, two older designs. I have been trying to find some detailed and specific plans to modify them, but I don't know if anyone does that here.