I bought this C9ii amp to pair with my Cayin N7+ and 64 Audio A18t CIEMs, specifically because the N7+ balanced output impedance is 1.2 Ohms, the C9ii is only .2 Ohms and 64 Audio recommends .5 Ohms output impedance or less else the bass starts to degrade. There are dozens of sound-shaping button options and this amp gives me bigger, yet still technical sound and really makes all my songs and genres extremely enjoyable... basically perfect. The Tubes are awesome. I bought the cover as well and highly recommend it. The only negative is that removing the battery cartridge has been impossible without the help of a second person. Luckily, I don't plan open replacing batteries any time soon. With both my N7+ and C9ii set to AB amp (which is my preference), both boxes get only slightly warm after an hour of listening. Set this way, they both will have well over 10 hours battery life. I also prefer the Modern tube timbre.