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As you've said, I love both amps.

The main difference between the EC 2A3 and Stratus is how "tubey" the sound is. The DNA Stratus sounds more like a traditional tube amp. It has a oodles of inner warmth, very dynamic, very good detail and very good micro-dynamics. The sound is lush, but not overly so as to impact other positive aspects such as clarity, articulation, bite, or excitement. It's an ideal balance between tube and non-tube. As others have commented, it works well with a very wide variety of headphones. I loved the DNA Stratus with headphones which tended to have an edgier treble. This includes HD800, TH900, Grado, Sony R10, etc. The DNA Stratus is also more intimate sounding than the EC 2A3. Think smokey jazz club. The one slight negative of the Stratus is the bass is a bit mushy. This can be remedied to a large extent with the EML 2A3 Mesh Plates, but it's still there to a small extent. In any event, I still love the Stratus with the Chinese tubes. And I actually like Donald's signature blue color (although some people hate it.)
 
The EC 2A3 is less tubey than the Stratus. Not quite solid-state as it still maintains a certain inner warmth inherent in the 2A3 tube, but more solid-state than the DNA Stratus. The 40kHz AC heater gets it very very close to the BA. The BA is slightly more detailed than the new EC 2A3 because of the BA's partial silver transformers. It's very very close and probably not noticeable unless you a have top notch source (which I don't think will be a problem for you). The staging and openness of the 2A3 is amazing - as good as the BA. The EC 2A3 sounds more "grand" whereas the Stratus more intimate. The bass control on the 2A3 is much better too (especially given a recent PS change to a stiffer diode). Almost as good as the best solid-state. The downside of the EC with something like the HD800 is that a little bit more tube rolling and/or HD800 modding may be necessary (methicks the stock HD800 is too bright and dry.) Ultimately, I think it comes down to precision/openness (2A3) vs. intimacy/lushness (Stratus). I want to stress that the DNA Stratus has nowhere near the extreme warmth, lushness, or syrup which I have heard with other tube amps such as the Carys, Lebens, and even the Woos.
 
The EC 2A3x4 will be more similar in sound to the 2A3. So if you don't like the EC sound and prefer something slightly lusher, it's not going to matter. I haven't heard the production unit, only evolving prototypes. But the the EC x4 should destroy the BA. Although the x4 uses larger OPTs more suitable for HE speakers or power hungry orthos (larger is not necessarily better - we want OPTs to be sized accordingly to the transducers as much as possible), the OPTs will remain partial silver on the secondaries. The main improvement on the x4 is the elimination of an interstage cap. This provides a HUGE improvement in speed, clarity, layering, and detail. Especially detail and layering. Literally, I've heard "shit" I've never heard before (and this hasn't happened in a LONG LONG time for me since I've pretty much heard it all.) Doubling the tubes also helps with power/current. I think Craig realized that the BA's power wasn't cutting anymore with some of the power hungry orthos out there. I had a prototype/test unit x4 (using similar 45 tubes) in my house, and I am missing it terribly. I have calls to Craig every week to see when the x4 will be delivered. It's easily worth it. I think Craig will be providing Psvane tubes included in the price. Best to put your name on the reservation list because I know the entry level price < $4000 including tubes will not last past the initial run.