Germanboxer, do you think reinserting a tube pre-amp would ameliorate some of what you are missing, particularly lower midrange density? I know you have already done that experiment, but...
I researched the Halo along with Prism Orpheus as possible DAC/pre-amps to front an Emerald Physics system. The word on the street at that time was that the Halo was more lean and mean but "true to source." The Orpheus was a little fatter and more euphonic. I never heard either, but that was what I was told by folks who had done the shootouts (whatever that is worth). I also dialogued with Barry Diament (well known recording engineer) and he used the ULN-8 in his studio and loved it and felt it was very true to source. No embellishment. That aside, I know many feel that the Metric Halo and Berkeley dacs are too "digital" sounding and converted to tubed products like the Lampizator. Gary felt that way even with the Atmas and later Tenor OTLs in place.
Then there is power (and Spiritofmusic, it rules indeed!). IMHO, that has more impact than people realize especially in terms of 3D presentation and even making things more "analog." I know the ULN-8 has a switching power supply, so I wonder about its effect on the sound and/or its potential imperviousness to power cords, conditioners, etc. Barry Diament told me that he experimented with tricked out linear supplies on the Halo and it did not make a hill-of-beans difference. So, I don't know what to say on that one. I "think" or "know" that dropping the noise floor and dealing with ambient inerference (RFI, etc) is important. I played with isolation transformers briefly (Topaz) with my EP system, and they had an undeniable effect. More clarity, dynamics, etc. I think they are a grand idea if you live in a crappy hood with lots of external garbage like industry, etc. Some people (who made use of transformers in the 80s) felt that they have a "sound" (which I think I heard) and can limit dynamics. I do not know or pretend to understand the technical particulars behind that. Another area of interest for me is grounding schemes. I have audio buddies who own the Tripoint Troy grounding system and cannot live without it. I also know several people who have made use of ionic grounding units in their homes, and they are purported to drop the noise floor significantly through grounding of your subpanel, outlets, and even the chassis of your equipment. One friend told me that an the sound of an average tuner improved dramatically! I will be trying this myself in my listening room that is being built as we speak. Then there is Dale's magic box, but more on that later in a different forum.
Don't forget your computer. While being a great source from a utilitarian point of view, it is a rats nest of noise and interference. There is a lot you can do, including linear supplies, shielding, hacking the programs that operate in the background, etc. MachI is one outfit that does mods. Here is a good discussion of some of the issues at hand: http://www.lessloss.com/page.html?id=45
Finally, I do hope you find bliss in the 4s and the right amp. That would make things a lot simpler and this meditation null and void.
