I received the JDS Labs EL Stack a few days ago, and have been using it since. I'm gonna give it a couple weeks before I post a full review, but I think my initial impressions might be helpful to some.
I really like the matte black minimalism that they employed when designing these. They pair very well, and sit square with each other. The copper ring on the amp is a nice accentuation, and it glows white when powered on. The amp has a power button on the back, and the DAC has a touch sensitive button up front that is held to power on and off. When on, that button serves as a switcher between the DAC's S/PDIF, USB, and coaxial inputs.
The DAC can handle up to 32-bit/384kHz through USB, which is much higher than my ears can distinguish, but is a nice convenience for those seeking as-close-to-bit-perfect audio as possible. The output of the DAC is sent through an RCA cable to the amp. The amp has an RCA line-out that automatically detects when it is playing through that output, as opposed to the 1/4" up front, and will automatically max out that output upon connection to it.
The 1/4" is a little gripe of mine. When trying to connect a pair of headphones, you have to insert the jack exactly straight before it will go in. This isn't too much work, but it's just something I noticed during use.
The knob up top is very smooth and, however weird it is to say, very satisfying to use. The amp is very powerful at 1.5W at 32Ω, and had absolutely no trouble pushing any headphone I threw at it. I had to be a little bit cautious not to blow out my HD 598s as this can get them very, very loud, without introducing much distortion.
Cursory sound impressions are that, well, it sounds great. The power alone is greatly appreciated, as there is more than enough headroom for pretty much any headphone I can reasonably think of. It's spacious, clean, and introduces no unpleasant distortion.
I'm going to reserve more commentary on sound until I have spent more time listening analytically and until I have a much more refined feel for this setup.
Thus far, I am very much enjoying my time with these, they pair very well and I have no major complaints.