...just a further note after 24hours burn in...
Well, already things sound noticeably different. That initial slightly "digital" sound, I guess I'd call it, that had me wondering if my tube amp is smoother, has gone. Unfortunately I cannot compare the DAC to anything of significance like Benchmark DAC 1 etc, but my impression is that there really is incredible detail. If I was to describe the effect visually, I'd liken it to the effect of an HDR photograph - where suddenly you can see the details inside the room, and outside the window at the same time - whereas previously the details through the window were burnt out white and not visible.
One thing I can compare is the 4pin vs 1/4" jack. When I listen to the HDVD800, I'm instantly made aware that there's an incredible amount of new "technology" going on in the box that I'm not aware of - I say "new" because it's the likes of which my ears have never experienced before - and it this phenomenon seems most obvious to me when switching from the 1/4" jack to the 4pin. Luckily I can run 2 sets of Cardas Clears to compare - one on 4pin and 1/4", and it suddenly occurred to me it's almost like Sennheiser has supplied a 1/4" socket (which sounds superb by the way) simply so that people can listen to the amp before they make the most obvious, and essential and absolutely inevitable decision to upgrade to 4pin. It's like just when you thought everything sounds clear, the whole system instantly elevates to another level.
And then I compared it to my Earmax SE tube amp - I did this running from the balanced Pre-amp from HDVD800 to the Earmax SE via Cardas Clear interconnects. So the comparison here is the Senn Amp vs Tube Amp, of course both use the Senn DAC. Well, the EARMAX for sure, has never been treated to so much detail and really sounds sublime, and if this was you're setup you would be surely be happy with whats going - and possibly (as a non-expert) satisfied that the sound couldn't actually be improved upon.
And then I switch to the 4pin on the Senn. To try and describe what I feel is happening, and this may be a bit daft, but it's kind of like I can suddenly perceive what the low/zero distortion that the HDVD marketing is referring to. And it's definitely not just a suggestive thing from the marketing, but rather I feel like it helps me verbalise what the profound difference is. So, the Earmax sounds absolutely clear and tight - running the funny EAT Dampers to remove microphonics etc, but then on the 4pin, it's suddenly like Earmax is somehow fuzzy around the instruments in comparison - like there's a kind of distortion there around the instruments that I couldn't see before. And now there's almost unimaginable clarity.
So just in case my opinion is any help to anybody, if you asked me if it's worth the wait and the price, I would already say absolutely. My overall impression so far is that this box has been specifically designed for the sole intention to showcase HD800. Obviously I'm no expert, but my overall impression when I walk away, is it so obviously apparent that Sennheiser is determined to establish the HD800/HDVD800 (4pin with third party cable) as the Orpheus of dynamic headphones.
(Which I guess is a bit of a bonus seeing as I purchased the headphones, custom cable 4pin cable and HDVD800 without audition) Ha! :)