Hi Benny, Really small tube amps like the Decware Zen prefer speakers with as low impedence (z-max) as possible. Any of the Pi Thermonic series will work, as will the Theater 4 PI model. Avoid the Pro series as they prefer to see at least ten watts per channel. I think you will find this forum to be fun and educational. Browse around a bit; there's a lot of information about Pi speakers with single ended tube amps. Take care, Steve
For what it's worth, I tried using an SE84CS with Thermionic 4 Pi's and didn't like the combination. Also for what it's worth, I sold the amp and kept the speakers.