Auralic makes the Aries G1 and G2 streamers that have digital outputs. On those devices, you would need to control the volume using an app on an iPhone or iPad. HIFI Rose makes the RS250 streamer, which has a digital output and a volume control knob along with what appears to be a very nice touch screen interface on the device.
Most streamers that you would get have apps that can control the devices as well as user interfaces on the devices. There are plenty of reviews of these devices on YouTube that will give you a very good idea of what the various user interfaces and features are all about.