it's so hard to describe these minute differences.... The Theta sound is fuller (has more meat on it) in the upper freq than the Wadia. I prefer the Theta top end to the Wadia in my Wilson system, if I had other speakers that weren't as fast or revealing the Wadia/Levinson might be a better match. I can't speak about the GNSC modification but when I was looking I was considering the Wadia 861 or the Theta Gen VIII. I felt the Wadia concentrated on the edge of the note more than the sustain...delicate but too delicate compared to live performance but more natural than the DCS,Levinson,EMM, etc.. If you like what the Wadia does then the new 581 SE sounds like an amazing machine that you might consider... it takes the hassel out of finding a good transport, but I have heard the Wadia still benifits from a good preamp... uggh... around and around we go..... I have huge depth of stage with the Gen VIII but not the width of soundstage in my salamander rack, but my dealers Gen VIII has huge width also in his Particular Rack, and I had it before I went to the salamander rack. I have tried a nice VTL 6.5 preamp which gave me even more air to my system so that it approached my dealers setup (without a preamp)... It might be as simple as powercords though also, as I'm running Purist Audio and he is running either Transparent or Shuyanta power cables. Both of our systems are running Transparent cabling for interconnects and speaker cables, and both systems are using Theta Citadels.