Weiss Helios - I have had this unit in for several weeks and have spent time with it. A few things stand out. The unit is obviously much larger than the 501. It is 2x the price of the 501 so the question is, is it worth that upcharge. Obviously that is a matter of your budget and ability to pay the list price of $21,999. If the price tag is in your range, this thing is fantastic.
The two things that are most noteworthy about this DAC is the depth of image and detail/instrument separation. In my system, I have not heard another DAC deliver the depth of image that the Weiss delivers. It also has extraordinary instrument separation. To a point where I have not heard another DAC this good. It is also more neutral than the 501/502.
This DAC carves out its own space in the price range. It is slightly brighter than the Playback MPD8 and maybe is more truly neutral than the MPD8 which I beleive drifts just a hair warm. There is a structure and stability to the image that is unlike anything I have heard. I historically have said no one is better between the speakers than Chord. This DAC is a step up from Dave and MScaler in my opinion. It also delivers an image beyond the speakers. The scale is not the same as Aries Cerat or Rockna but is still great.
Instrumental separation and the detail within moments like the drum rolls are extraordinary in In a Sentimental Mood. The absolute scale of the soundstage in Be Still My Beating Heart was not as extraordinary as the Aries Cerat or EMM but it is great. Noise floor is quite low.
Liberty is smooth and clean. Effects come from well away from the speakers. No sibilance at all. The opening of Duende is clear. This is the cleanest and clearest I have heard the bass solo. There is no smearing at all. Separation of strings in the berg piece is just extraordinary.
This unit falls in a middle ground between Playback and Aries Cerat. It is not as big and dynamic as Aries Cerat. It is not as soulful and sweet as the Playback. But it is in this amazing middle ground that is enjoyable and really special. Best for folks where image structure and stability along with detail are primary concerns.