I think Wavelength offer something like this.
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I own the Cosecant, it is a non-upsampling USB Zero Dac, with a Tubed output stage. And like Paradales said there is a version that can act as a Premp with Volume. Actually Wavelength now has 3 different USB Dacs in the line-up, with varying versions.
There are others like the Bel Canto, Musical Fidelity, Benchmark, Hag to name a few. However other than the interface they are completely different in their design/philosophy;`using primarily commodity based DAC chips, upsampling, filters. The Wavelength DACs are a custom made product from the ground up, USB controller custom designed, power supply as well and so on. The sound I have experienced from Cosecant is mind boggling, from Brick sound is superb for the money.
From a design and research standpoint these products are simply incredible and have no equal at the moment. Here is the link to the site...