Nelson has created a storm of interest with the Zen I/V.
I have a DAC that I can use this with, a K&K RAKK DAC Mk1.
Currently, it has a passive supply and a switchable shunt resistor.
So I am brainstorming on what it would take for an active Zen I/V with a shunt volume control, and both SE and Balanced outputs.
Basics: PCM1794 has differential outputs with 8 ma current output.
So I need 2 Zen I/V per channel.
At present, I am running a DCX2496 Digital crossover, so balanced outputs are a plus.
I am considering using the buffer from this post.
Since bipolar supplies are required for the I/V section, a buffer that does not require additional caps seems prudent.
For the volume control, either http://www.kandkaudio.com/linestage.html
Shunt Stepped attenuator or a single LDR replacing the K&K unit.