@shaney777
I wouldn't get caught up by what folks at Head-Fi say - there's plenty of audiofoolery going on there. Solid states are superior to tube amps at, well, amplification (taking the signal, not messing with it and amplifying it) - simple as that. People that don't bother spending money and like collecting gear might like to have some tube gear - others might enjoy the particular flavour of distortion from tubes and then tube roll to get just the right kind of sound for them - but it's just that, distortion - go for clean sound, especially when just starting.
JDS should do fine, but if you want a bit more power at a similar price then look at Schiit Magni 3 and Heresy + their Modi dac. The newest versions measure well (even though Schiit does some bad measuring shit and can be jackasses).
In my experience, the Sundara is more open (simply due to build) and leaks more sound than Sennheiser, but also has a bit more pronounced treble and the HD600 will be smoother in that regard. I won't say the Sundaras are piercing in the treble, but if you're sensitive to those sorts of things, you may come upon some peaks form time to time. Obviously, if you're up for EQing then you can tune to your preference.
Ideally, you could get both, try them out for a week and return the ones you like less.
In my experience a good way of going about things is:
1. Look at measurements and don't believe golden eared audiofools with fluffy language and ill-defined, inconsistent terminology
2. Using measurements and your budget - narrow down the selection
3. If possible - demo the selection - there's a lot of stuff that matters - comfort for you personally, the build quality, even looks - for example, the AKG371 are a good measuring, affordable closed back - but I just can't use them because for me the fit is not good and I dislike the build intensely
4. Give yourself some time - I found that over a sufficient time span I notice I'm grabbing one piece of gear more often than another and if something is not being used it's time to sell/return - now, if you don't have the luxury of time - you'll be fine since you started out looking at good measurements
5. Dial in your taste - you may prefer more bass, more treble, or less of both - if you start off with good measuring gear you can dial in your taste via EQ - this is the point that most subjectivists can't seem to get - they want "flavour" but they seem to want it in their gear - which is all fine and dandy if you have money to burn and really like spending on gear - just not the way most people should do it.
Obviously, most of the people here like the hardware itself - not just enjoying music - otherwise we wouldn't be spending so much time, effort and money in this hobby - but my advice is for that balancing act to favour listening to music (or enjoying other sound - e.g. movies, games) as much as possible - you'll find you can get good, clean gear for not a lot of money and enjoy your music just fine. Once I started making this thought prominent in my mind - I could more easily sell stuff I wasn't really using (e.g. Focal Clears, and all but one AMP and DAC), and I feel like I don't have to chase the next great thing. Some of us learned by making mistakes and starting off as audiofools - probably best to learn from our mistakes rather than making your own