David, good call, and I should have clarified. While most of my listening is to Spotify Radio/cherry-picked songs from Spotify, I do use JRiver > DSD > WASAPI > Loki > headphone amp and I have about 30G of high-rez FLAC and 24/96 material to go through at work.
The Senn 650's maiden voyage, if this helps, was Brothers in Arms, 24/96, followed by Norah Jones > Come Away With Me. I have listened to both songs extensively on my home system and with my Grados and I knew right from the beginning the Senn's are good cans, and despite not being touted as "rock-centric" like the Grado line always is, I do prefer them on Rock. Rock and metal can get fatiguing quickly, especially depending on the source, so things that are less forward in some areas (up top) but still warm in the midrange give me the most satisfying experience. I still want a little more lowend but hopefully the Ember II takes care of that after it breaks in.
And I will wholeheartedly agree with you, Spotify Premium IS better than Pandora (IMO) but it cannot compete with lossless in any way shape or form. But, I only have so much space for music and my High-Rez collection is about 300G so I have to pick and choose what I take.