The Meitner modification of the Philips SACD-1000 involves the installation of a circuit card in an unused space on the left side of the player. It is (primarily) an optical interface, with individual AT glass fiber outputs for encoded DSD digital data, and also input/output for digital clock. As noted, the Meitner board also provides an AES/EBU (balanced) digital output, for unmodified PCM digital 16/44 only, and the Meitner-modified SACD-1000 could be used as the transport for any DAC accepting a balanced digital input.
The magic happens via the AT glass outputs, when partnered with the Meitner DAC 6, or new DCC-2 DAC/preamp. Together they are absolutely the best digital source I have ever heard, whether playing SACDs, or PCM discs upsampled to DSD. It does not sound remotely "digital" as we have come to use the term, but (at least) an "order of magnitude" better. There is a complete absence of artifact, edginess, irritation, glaze, congestion, harshness, grit, or however you may characterize the entire catalog of unnatural and fatiguing digital distortions, however subtle; they are simply GONE.
If forced to use a single term to describe what most impresses, it would be the overall smoothness of the presentation. To my ear nothing is lost, and the reproduction of nearly everything is improved: air, ambience, space, soundstage depth & width, natural detail, dynamic range, micro and macrodynamics, truth, beauty; I'm sure you get the idea. I am confident that anyone listening to the Meitner gear will recognize the "rightness" of the sound at once. IMO, it is as true to the "Real Thing" as anyone has yet approached in the digital reproduction of music.