I totally forgot about this thread, since I did not get any replies when I originally posted in 2014. Interesting this thread picked up a bit. In a round about way, a dealer sent me a PM this morning, and referenced this thread, which is the reason I even found it again now.
There have been some changes to my setup since I last posted. I am currently using a Aqua La Scala mk2 with a Tortuga LDR passive preamp. Although the La Scala is very good, I feel it is not resolving some details, and the high end appears slightly rolled off. The presentation is a tad forward for my taste as well. Of course, there are a whole lot of positives to list about this DAC too. I'm also not completely sure that the passive preamp and/or cables may not be causing the rolloff and lack of detail. I haven't played around with my setup much to see. In comparison, my old Resolution Audio Opus 21, with GNSC upgrade, (going direct to amp) does not exhibit such deficiencies.
I'm in the process of trying out an active tube preamp (Linear Tube Audio MZ2-S). It is on order, to be delivered some time this month. Once I get this into the fold, I will evaluate the passive vs. active preamp situation in my setup, and I'll be better able to tell whether the deficiencies I've noted are related to the DAC or elsewhere.
I've also tried a Vitus RD-100 (direct to amp connected), and although it is very good as well, the sound stage was a bit narrower and less spacious than with the Aqua in my setup (Aqua going through passive preamp). The dealer I bought the Vitus from said he was using an active preamp with it. In my brief listening, I also felt that the Vitus would open up with a good preamp behind it. Since I still have the Vitus (haven't been able to sell it yet), I'll probably try it out again with my active preamp.
So, in summary, I'm still looking for the right combination of front end pieces. I'm still looking to try out a few more DACs in the process as well. Since I have a few more pieces of audio gear than when I started out on this journey a couple years ago, I have a lot more options now. Of course, I would still prefer the most simplistic DAC to amp setup, for cost and other reasons, if I could achieve the best sound that way too.