@Cyan69, let’s return from our journey down memory lane with our Walkmans (Walkmen?) and old receivers and stay on task. Can you go over your current audio chain again, but this time be very exact on how you are connecting each component? Describe each connection individually.
My feeling is that you should keep your Sundara right now, and use some of your $2000 budget to buy a new DAC and amp. The Sundara is a good headphone, certainly good enough to test your replacement DAC and amp, to make sure it sounds the way you like it. If it doesn’t sound good with your Sundara, then it probably won’t sound good with a more expensive headphone. As others have mentioned above, you should be able to buy something good with a $200-400 budget. Given that, let’s try to figure out your audio chain, and what can still remain vs needing to be replaced.
You mention having DSD, Flac, Amazon HD. I’m assuming that is sourced from your PC. What are you connecting your PC to, and using what kind of cable? And what software are you using to play your music - Foobar, JRiver, something else?
What are you using your OPPO-103D for? How is it currently connected? Do you want to keep it plugged into your Denon speaker system and also your new headphone system?
Is your Denon receiver used for AV/movies, surround sound music or just for 2 channel music, connected to 2 speakers? The Denon is a good receiver for AV, and you should keep it for that use.
I’m wondering what are you currently using as a DAC right now, in particular to process the DSD files. I don’t think the Denon processes DSD, and if that’s the case, is something in your chain converting DSD to PCM?
Guys, is DSD playback key to the eventual solution? I don’t have any DSD files, so I don’t know if Cyan69 has to buy a DSD-capable DAC (e.g. the Schiit DACs don’t process DSD) or if something like Foobar can automatically convert DSD to PCM, in which case any DAC can be used.