Here is a "little" comparison done on the same dac between the PMD-100 (HDCD) the PMD-200 (HDCD) and the very highly regarded DF-1704(non HDCD)
Results Listening Comparison Of Digital Audio Filters
"It's worth noting that the differences between filters became more obvious after hearing the PMD-200. Its very high sound quality helped educate our ears to the new range of resolution possible. It also helped to have listened to the PMD-100 in this equipment configuration over more than a year. This gave a solid basis for comparison, and made the differences far more apparent. While the DF1704s sound was noticeably different from the PMD-100 when first compared more than a year ago, the differences are more pronounced and obvious with a more familiarized and better educated ear.
Comparing the PMD-100 to DF1704, the 1704 was harder, grainier and generally sounded like it had less resolution. Applause at the end of Hotel California on the Eagles' reunion album was harsh and unpleasant on the 1704 and much smoother and "rounder," yet clearer and much more distinct on the PMD-100. On Hotel California and Wasted Time, kick drum, piano, voice and string sound was much more convincing, natural and pleasant on the PMD-100. Applause leading into Tequilla Sunrise was much softer and more natural on the PMD-100 than DF1704. Vocal and instrument sounds were much more natural, "round," and pleasant sounding. The PMD-100 portrayed more detail, decay and space around the gong and tympani on Copland's Fanfare than the DF1704. The 1704 sounded more artificial and "hifi", grainier, veiled and less clear. The PMD-100 again sounded more natural. The horn recording on the Copland disc has a few audible flaws (probably digital recorder or microphone artifacts) but was generally better on the PMD-100 than the DF1704. Margo Timmons voice, bass, and percussion sounds on Trinity Sessions were more realistic and detailed using the PMD-100. Trinity Sessions' reverberation, a strong point of the recording, was also more natural on the PMD-100 than on DF1704.
Comparing the PMD-100 to PMD-200 I was struck that the PMD-200 is vastly better than the PMD-100. To put it bluntly the PMD-200 blows away the PMD-100 in terms of resolution, detail, harmonics, reverberation, soundstage clarity, openness and image localization and snap. The 200 makes the 100 sound fuzzy and grainy in comparison. The PMD-100 is comparatively vastly superior to the DF1704, so the PMD-200's strides towards great sound are that much more impressive. On Fanfare, the PMD-200 presents tympani membrane sounds with vastly more clarity, and the gong's metallic sounds, harmonic changes during decay, and vibrato modulations are also much clearer. It's as if you can hear what's really going on within the metal and drum membrane. String and piano sound is also much clearer using the PMD-200. In a visual metaphor, the PMD-100 seems like an realistic painting versus the PMD-200's photograph. Hall reverberation is more clearly recreated with the PMD-200, resulting in a more spacious, open and natural sounding room. On Timmons' voice and Trinity Sessions instruments in general the PMD-200 brings forth much more spatial and harmonic information. Decay of rim taps is much cleaner. Room sound is more obvious and clean. The general sound is more natural and realistic.
The difference between these versions of Pacific Microsonics filters is of a different kind than the difference between the PMD-100 and DF1704. Given that the earlier PMD-100 and DF1704 filters are from a closer generations while the PMD-200 is based on a fairly powerful 100 MIPS Motorola DSP, this performance gap seems reasonable. (The DF1704 is actually a later design than the PMD-100, so it should have had the advantage of newer technology.) The DF1704 is also based on completely different design principles. PMD-100 and PMD-200 do some of the same things well, mostly in naturalness of sound, and come from some of the same designers.
Switching back to a comparison of the older filters, a few audio writers have expressed a preference for the DF1704 over the PMD-100. I would describe the DF1704 as harder and more "hi-fi" than the PMD-100, which to my ears sounds far more natural. The brain is marvelously adaptive; it's what makes humans survive and thrive. Is it possible that these listeners have become accustomed to the harder "digital" sound that the DF1704 produces and have come to associate it, perhaps subconsciously, with "quality"? While that may be an open question, I prefer the naturalness and apparently cleaner resolution of harmonics of the PMD-100."