MidFiMoney
500+ Head-Fier
I never had the 800 S, but did have the 800 for a period of 3 years before owning the Utopia -- definitely have put the hours in on the Senn's lol. When you say detail retrieval, I take that to mean how audible each frequency is, and or the ability to hear and separate every noise that was recorded in the source file. Let me just say that prior to the Utopia's, my floor standing speakers, the Triton 1 by Goldenear, was my 'reference' for sound. My combination now of the Yggy+Rag+Utopia has become my new 'reference' -- audio has never sounded so transparent and good.
In my experience, the HD 800 does not resolve detail as well as the Utopia. I don't have the words to correctly describe it, but at least on my set, the 800's would definitely blend more sounds together and lacked the imaging of the Utopia (not to be mistaken with soundstage, where the 800 has Utopia beat). For better or worse, on the Utopia it really feels like I can hear and make out just about everything in the source. The only instance where I have trouble with imaging is in tracks that have a lot of low frequencies playing simultaneously, and in these cases it feels much more in line with the 800.
So as someone who has put in very, very many hours on the 800's, the short answer to your question is that the two are very far apart in favor of the Utopia.
You articulated what I meant by detail retrieval better than I could have haha. I suspected the Utopia to be more detailed but so many people are confirming the difference is rather significant. This is well after the hype, mind you. Thanks for your input!