Pros: A great companion to the HD 800, plenty of inputs and ouputs, looks nice
Cons: Not ideal for low ohm headphones, the dac sounds no better than mid-range gear
Having owned the HD 800 for more than three and a half years now I've spent untold hours looking into ways of bringing the best possible sound out of them. When Sennheiser announced the HDVD 800 it made my future upgrade decisions easy. I took the chance of being an early adopter, getting it before any reviews were out and hardly anyone had even posted impressions. Now several months later I feel comfortable expressing just what it's really like owning in practice, and how it stacks up to other gear. My perspective might be a bit limited, as I haven't heard nearly the same scope of gear as other more well known head-fi posters, but I've heard enough that this should at least be somewhat useful to someone considering the HDVD 800 or other similarly priced gear out there.
The HDVD 800 is Sennheiser's all-in-one balanced amp and dac combo for HD 800 owners. Sennheiser has done things to optimize the amplifier in the HDVD 800 for the HD 800, such as tweaking the output impedance to 43 ohm, as that tilts the sound balance slightly as to give the HD 800 a bit more bass oomph. The downside of upping the output impedance like this is that low ohm headphones like IEMs can start sounding quite muddy and overly bassy. How this affects any pair of headphones depends on its impedance curve, so have a look at the pdf charts on innerfidelity.com or headphone.com if you're worried about that. Headphones where the impedance is a straight line, like the Audeze LCD-2 shouldn't be affected at all by this.
So finally on to the important bit, how the HDVD 800 sounds. When it comes to the HDVD 800 amplifier section (I'll get to the dac later) I think Sennheiser nailed it. I've never heard the HD 800 sound as good as it does with the HDVD 800, and it solves the problems I used to have with the HD 800. It has nudged the sound in the right direction as to make them highly enjoyable to listen to over long periods, without me ever thinking the sound is too cold or analytical. I used to own the Violectric V200 which is touted by many as the ideal companion to the HD 800 as it has a smooth top end. The problem with the V200 is that the smooth sound comes at the price of a seriously compromised sound stage. Instead of the sound stretching far outside your head and creating the illusion of the music existing as separate layers with "air" between them, the V200 creates more of a flat sound that exists close to your head. At the same time as I owned the V200 I also had the SPL Auditor, which produced an enormous soundstage as I described above, but the Auditor had the problem of sounding a bit too cold and sterile. Music just didn't sound quite natural with it, so I constantly switched between the V200 and Auditor, not being completely happy with either. The HDVD 800 thankfully sounds much better than either of those amps ever did. It has the big soundstage, and it also has the natural tone and balance. Best of both worlds, and not inferior in any way to either. Simply better.
Then we get to the negative parts of the HDVD 800, the dac. For the price you might expect to get a "end game" solution, where neither amp nor dac leave anything to be desired. This isn't the case with the HDVD 800 though. Where Sennheiser put the most effort and money is on the amp, and that is clearly audible when you plug other dacs into the HDVD 800 and compare. The markup going from the HDVA 600 to the HDVD 800 is about €300 where I live, and the dac in the HDVD 800 sounds about as good as a €300 dac. I compared it to a Asus Xonar Essence ST sound card which uses a the same dac as the HDVD 800 dac, and the results were nearly indistinguishable. The HDVD 800 was slightly more refined and smoother in the higher frequencies, but I had to listen for it. The first few seconds there didn't appear to be any difference. Not exactly the result you'd want.
When plugging in a higher priced dac like the Violectric V800, Xonar Essence One Muses Edition or Hegel HD10 the HDVD 800 dac starts sounding like an insult to the amp it's attached to. The balance of the HDVD 800 dac is well suited for the HD 800, as it's quite bassy. On first listen you might actually like the dac a lot. But when you live with it for months like I did the limitations start to become a bit too obvious. The soundstage is always about the same size, and instruments are in about the same place, no matter the recording or artist. And the bassy sound which is nice at first comes at the cost of detail, as the bass is "one note", ie vibrating bass strings sound muddy and indistinct, while a better dac with the same amp suddenly makes the same bit of music actually sound like a vibrating bass string. With a better dac the subtle difference between all recordings are laid bare, and it becomes a greater pleasure listening to music as you can pick out every single little detail which makes the tracks unique. With the HDVD 800 dac many details blend together and are obscured, so you end up with a limited range of possible sounds you can hear. I often see reviews of great gear where the author describes the gear as "getting out of the way from the music". It's one of many audio review phrases that makes me groan, but in the case of the HDVD 800 I feel it's highly appropriate to turn the phrase around and say that the HDVD 800 dac gets in the way of the music. There's just so much great sound to be heard from the HDVD 800 amp that you won't hear with the dac it comes with. Unless you have serious space limitations I'd recommend getting the HDVA 600 instead and then taking that money and saving up for a better dac in the ~$1000 range or more, since that would bring you significantly better sound.
Overall I'm happy with how the HDVD 800 is making my HD 800 and LCD-2 sound. As an amp it sounds wonderful, and the fit and finish goes well with the HD 800. They look and sound like they belong together. If only the dac was better I'd feel more comfortable giving it a recommendation without reservations. As it is now though I'd recommend listening to it first if you can, just to make sure you're ok with how the dac sounds. If you're a bit unsure I'd recommend the HDVA 600 instead, as the amp is identical to the HDVD 800, just without the dac section. It lives up to what I'd want a high end headphone amp to sound, look and feel like. If only the dac was a bit better.