I have heard one in another system and they sound good. I use single ended el 84 tubes for my foil tweeters, and the single ended el 84 sound the best of many different amps that I tried, varying from solid state, push pull, DHT etc..
The Decware Zen is also not fussy about speaker impedances. You can pretty much sell it for what you paid used anyway, so it is worth a try, I can't imagine needing much more for the high frequencies.