Stereo DAC - or D/A Processor, as they like to call it.
We like Schiit. According to Stereophile, here's what they have to say about upsampling:
"Not just no but hell no. None of our DACs will ever do sample rate conversion. Our goal is to perfectly reproduce the original music samples, not to throw them away and turn everything into a mystery-meat soufflé. . . . We worked hard on a microprocessor-controlled, bit-perfect clock management system to ensure that all the original music samples going into Bifrost are delivered to the D/A converter. . . ."