I have them, but they are just passive speakers like many others. That means you need a speaker amp for them, they don't have a built-in amplifier (basically like regular wired headphones). If you use them with a power amp, you can use some existing volume control you already have (say a DAC with built-in volume control or maybe the OS volume setting into your DAC), or a preamp to control the volume with (which could be as simple as a Schiit SYS or a headphone amp with pre outs). Alternatively you could use an integrated amp (essentially preamp + power amp in one box). Either way, you need something to control the volume with, a power amp typically has a fixed amount of amplification and at best a difficult to reach gain adjustment that's more intended for volume matching with other amplified components (like a subwoofer or another amp in a bi-amping scenario).
They can get really loud, though, so I'd avoid something with a pure software volume control that some software could reset to 100% without you realizing it before you blow your ears and annoy your neighbors.
What gear are you planning on using them with? Nice choice, BTW, I love mine.