The Meitner DAC is excellent when upsampling Redbook CDs, in my experience. I used it for a few months as a stand alone while waiting for the CDSD to arrive, with a Sony DVP-9000ES as transport. The CDSD with the DCC2 or DAC6e is a significant improvement, and IMO state of the (digital) art, as noted by the previous posters.
However, I was able to markedly improve the performance when using the Sony 9000ES, by first upsampling it's digital output with a Monarchy 48/96 unit, and then via the Monarchy's AES/EBU output to the Meitner DAC (as crazy as that sounds.) The Monarchy dejitters, upsamples, and also boosts the gain, (and the increased gain alone may be a big factor) but it was an across the board improvement. I had previously used the Monarchy 48/96 in the same manner, with a Theta Gen Va 24/96 DAC, to similar effect. To give proper credit, this method was suggested by Marty DeWulf in "Bound for Sound", and the upsampling/preconditioning of the digital signal before the DAC is a clear winner in my experience.
The Monarchy 48/96 has a coax and a toslink input, and a coax and AES/EBU output. Other upsamplers that can also be used in this way include the Camelot Dragon, (Marty DeWulf's favorite) and the Assemblage D2D1, both of which offer more types of digital ins and outs for digital format conversion as needed.