In my search for a tube preamp, I came across a couple with USB outputs! I am curious if anybody here has any experience with these? Here's the most interesting one.
HIFIMAN EF2A USB Headphone Amplifier
Both USB & Analog Inputs The EF-2A sports both a stereo analog input and a USB B-type input. Switchable from the faceplate. The analog input is very good in its own right offering astonishing transparency for such an inexpensive product. The USB input allows the EF-2A to make use of its Burr Brown PCM2702 D/A converter and offers far greater sonic performance from your computer than using the headphone output.
The DAC in the EF-2A supports up to CD quality resolution (16Bit/44kHz) via USB.
An affordable alternative in a tube-driven headphone amplifier, the EF2A is a hybrid design, USB headphone amplifier using 6J1 tubes for its input stage and incorporates a Burr-Brown PCM2702 DAC Chip. The EF2A provides USB input and features 16 bit 44.1 kHz performance.