Not possible. But it is considered transparent. As I have no comparison, I can't tell, even I use my 2 pro as a preamp with a phono pre connected.

Thanks for the replies and answer to my question. Too bad. I hoped for unity gain with volume control. I'll check out the ADI-2 FS.

Until very recently I had a complicated setup with an ADI-2 DAC and a Benchmark headphone amp just so I could switch between a couple digital sources (USB and coax) and a phono preamp and between headphones and speakers. I liked the idea of keeping the phono signal path pure analog, but it was annoying having to switch inputs on two different devices plus the extra space, wiring, etc. of that setup.  Also some things about the Benchmark annoyed me, like the constant clicking of the relay-based volume control and the difficulty of something as simple as toggling between headphone and speaker outputs.

I just replaced the whole setup with an ADI-2/4 and now one small box does everything I need perfectly.  I had a brief moment of panic when it first seemed that it was only possible to send USB to the headphone 3/4 output, but then I discovered the DAC mode didn't have that limitation and worked just as I wanted.  That and the fact that the remote doesn't work out of the box (you need to push the right buttons to switch the code table) were a good way to ensure that I RTFM despite my previous experience with the ADI-2 DAC

It's a brand new unit I just received from B&H.  It had the latest USB firmware and I think the DSP firmware was one revision lower than the latest before I updated it.

The remote came preconfigured for the green code table to work with the ADI-2 DAC.  The manual even says that you need to reconfigure the remote to get it to work with the ADI-2/4 Pro:

If you use AD/DA mode you can use the digital volume control to adjust the levels. It's - to my ears - fully transparent even @44,1kHz.