Your English is not bad and I'm french so... :D
I never listened to the Octave, that's why I was only making asumption for the Octave "alone" vs. Quad + U3 in a computer-based system (or, in my case, a Squeezebox Touch).
The two Metrum DACs differ in the number of DAC chips they feature and their power supply. Basically they supposedly have the same digital input stage, which is not really good at reducing jitter. Most of the Octave users tend to agree on that: it requires a good S/PDIF transport (either a good CD transport or a DDC like the Stello U3 or Audiophilleo). My findings with the Quad are similar in this regard.
You can find other inputs in the Reference 5.2 thread. I compare it directly with the Quad and shared my concerns regarding its lack of dynamics and PRaT (in stock version) on my setup. After a simple cap mod (remove 4 capacitors in the ACSS modules as presented in the user manual) these concerns were gone.
In term of technicalities (technicities?), they are in the same league, no doubt. They share a delicious natural tone that's extremelly enjoyable!
The rest is just a matter of preference:
- The Quad is more forward sounding, which, on my setup, is more involving and serves the music better. It is a simple design (small, 2 inputs, 1 output => that's it!).
- The Reference 5 is more prone to exhibiting its (many) strengths. As its name suggest, It is a "Reference" DAC. It has much more features (built-in DSP, many inputs, balanced outputs) but it is bulkier. The sound signature is slightly darker in comparison.
Overall, I must admit I prefer the sound of the U3 + Quad because it just plays music. Before that, I was expecting a DAC to exhibit its strenghts (resolving, focused sound, instrument separation and so on) to get that "WoW" moments. In this regard, the Reference 5 is the better one. In comparison, the Quad does not have that precise soundstage/layering, the sounds just come out from "nowhere" (I'm exagerating on this point, of course) but in such an enjoyable manner that I just don't care. I'm not saying the Quad is not resolving, it is (on par with the Ref 5 in term of detail retrieval), just that when I'm listening to it I don't try to locate the origin of the sounds, I'm just enjoying them coming at me in a very natural way. Like I said, the music just flows......
If I had bought the Reference 5 earlier, I probably would have had a big "Wow" moment and wouldn't have any urge to upgrade it. The thing is, I already owned the Quad for 1 month when I bought it. There was no big step between the 2, so no big "Wow" moment happened (and I wasn't expecting any, to be honest). I bought it for its many features and the matching case for the SA-31 headamp but I realized I don't need the extra features right away so I'm gonna sell the Reference 5.
Edited by Clemmaster - 11/28/12 at 5:50am