If Tidal continues to offer its wide selection of music and continues to acquire recently released material then I see no harm in Jay - Z's purchase.    It can only bring more exposure which will likely speed up the shift from traditional streaming to High-Quality streaming (which is the future). 

I have the Sennheiser Momentums I use daily on my way to work, metro, and around town and I love them. The sound is tremendous, and at home I pair them up with my Dragonfly DAC and the sound is amazing.    However, will getting the Sennheiser HD 598 and pairing it up with my DAC for home...

I'd go with the Sennheiser Momentums with a Meridian or Dragonfly DAC

Try using Tidal if you're looking for Hi quality audio files to stream. Waaaaay better than mp3s

Try Vox or VLC

  Naturally of course. So without considering money, how big of a jump is it from the setup I mentioned above? Dragonfly - Momentum to Dragonfly - 02 - hd 600 sound-quality wise. Is there a definite and improved difference in sound quality strictly and only technically speaking?

  Do you think the upgrade from Dragonfly-Momentum to Dragonfly - 02 - HD 600 is worth $400? 

Could I pair only the Schiit or 02 amps with a USB DAC? The Dragonfly is a DAC that is connected via a USB port.

Okay so sorry for posing this question for the millionth time but I'm new to this, like really new.    I have the Sennheiser Momentum which I pair up with my Dragonfly DAC to my computer and I listen to Tidal and some albums off of HDTracks. Nothing fancy, but definitely better than what I had...