Sprout 100 + HE-400se

Just a couple of weeks ago I got my Sprout 100. My intention is to use it as desktop DAC/Amp/Headphone amp. At the same time I got the HiFiMAN’s HE-400SE. At first glance, the Sprout seems to handle these pretty well, but since there’s no way to tell how loud the volume knob is on the Sprout, I’m wondering if it’s already at its limit.
Has somebody had some experience with the Sprout and high demanding headphones like the 400SE?