This is a quick review that basically sums up how I feel about the Atlas (HD 800S) and the Andromeda (HD 800):
A quick history with the Andromeda: I purchased this IEM after A/B'ing with the Jupiter. I enjoyed the Jupiter immensely. It was VERY engaging, but to me it sounded a bit too boomy in the bass where there was bass-bleed into the mid-range. I could best describe the sound-signature of the Jupiter as a big canoe. The Andromeda basically fixed this 'issue' by moving the mid-range WAY forward, but it also tamed the bass down and made it softer-sounding, yet somewhat punchy, thinner (it stood in the background in comparison to the mid-range and treble). I quickly sold the Jupiter.
I could best describe the sound-signature of the Andromeda as a space-ship. My god was it detailed! Wide! Fast! Super-speedy! Imagine a space-ship going through the universe .. the soundstage was endless. You knew something was out there in the far-out spaces, but you had to make a decision on whether or not you wanted to focus on whatever THAT was, and in the end this proved to be a give-and-take. When listening to the Andromeda I couldn't help but focus on the details, the schematics of the song being played. However, I felt that something was missing, something was too polite (the bass) and something was too emphasized (the treble). The light-speed travel was awesome, but it was almost blinding. Honestly, I'm getting WAY too carried away with these weird comparisons between sound and ships and the universe, but I'm too far deep to get out of it! The Andromeda is a great experience, but I felt that I was taking on the whole universe no matter what I was listening to and it proved to be overwhelming most of the time.
In comes the Atlas. The best way that I can describe the sound-signature of the Atlas is a pirate-ship. YArhh! I'm here to conquer everything AND I'm looking for the best that everything offers. It's aggressive, big and powerful. It knows how to navigate the sea very well. The crew is a bunch of ghosts that have been there and done that, been everywhere, seen everything that there is to see and now it just wants nostalgia, to feel alive again. The cannons go off, there's the presence of a crew member on the top of the mast looking outward and everyone is doing there job on starboard. But seriously, the Atlas just feels mature. It's more old-fashioned. I'm finally engaged with the music. I'd also like to add that the vocals are ON POINT! This is one aspect of the Andromeda that I couldn't handle (think sharp 'sssssssss' whenever I turned the volume up).. with the Atlas I am encouraged to turn the volume up.
A few other points: the cable on the Atlas is better quality (less tangle), the fit to me is good (although when I'm taking a walk it sometimes feels as if the housings with fall out, but they never do) and the Final Audio tips that it comes with are spectacular. Unfortunately I almost always had to adjust the Andromeda after every song and I'm not a fan of the over-ear wear.
In the end I decided to sell the Andromeda. I just couldn't get over analyzing every song rather than listening to it -- this is where the Atlas hugged me and never let go.