At the moment I have the Metrum Ambre for testing/comparing against my recently bought DigiOne. But I’m not impressed, of course it sounds good, but I would probably say it sounds the same as the digione.
Anyone knows where the € 1000,- difference is, or what should I do/test/change?
It’s in Metrum’s pocket. 
Not yet. 
It’s loaner for testing.
I try to stay on the cheap end of “plenty good enough”. And, I don’t attend Audiophile conferences that serve only to tease and torture. Ignorance is often bliss.
You’re right. But I can get this one (used) for a reasonable price, so I could loan the Ambre for a test at home, but not impressed by it so far.
I’d be amazed if there was any appreciable difference. Both stream the same bits out of the S/PDIF outputs, both use RPi 3B+ with another board for the outputs. I’d guess that if you have a good DAC, none of the additional stuff Metrum adds will be necessary, and if you have a bad DAC, you have other problems.
But of course hearing occurs in the brain, not the ears, and I know that some people just hear things they like better on a more expensive stack. So YMMV.
Marketing, distribution, sales costs etc. Also, Allo only had to focus on the DigiOne design, the Raspberry Pi and OS are not their responsibility.
I find that there’s not much between some Pi DACs and commercial DACs using the same integrated circuits.
Well, the Ambre has more kinds of outputs, if you can use them. It has more internal clocks, which may reduce jitter, but jitter apparently isn’t a real problem with good DACs, which re-clock their inputs anyway. It has optical decoupling between the main Pi board and its outputs board, which adds complexity (a bad thing – you need to add drivers on each side of the optical connection) but may address some hypothetical ground loop issues which in my understanding shouldn’t bother a good DAC anyway. So sure, there’s more there, but whether the extra stuff adds any value is a kind of open question, I’d say.
For now the only advantages I can hear here are probably the Tentlabs clocks. The timing is a bit better which makes voices more understandable and less vibration in the lower sections.
Timing errors of only a few nano seconds . … is that audible? As @Bill_Janssen says, good DACs will re-clock the input anyway. I’m surprised the Ambre doesn’t have 75Ω BNC coaxial input.
What it exactly is, i don’t know, but the only difference i can hear looks like a better timing. And I guess technically I can only imagine that it is because of the different clocks. (Tentlab vs NDK)
Strange example, hard to explain for me in English, but I will give it a try:
Sitting on the couch with my feets on the table, listening to “Hello Again” from “Neil Diamond”. With the DigiOne I feel a little vibration in my feets from the table, and Neil Diamonds voice has a bit of a hum. With the Ambre, his voice is more direct and a bit clearer, no vibration in my feets 
Also the voices are more understandable with the Ambre, it’s a bit more relaxed.
To be clear; it’s the DigiOne + HDplex psu and the Metrum Ambre, the cables and connection are the same.
The main board houses the TOSLINK, AES and i2S connectors. The SPDIF connector on RCA is remote, I guess for lack of space on the PCB vs product size. This has at least the advantage of being able to replace the RCA with a BNC for those interested.
“I find that there’s not much between some Pi DACs and commercial DACs using the same integrated circuits”
Would you mind elaborate on this part?
Sure. My first Roon endpoint was the IQAudiO Pi-DAC+. When I decided to upgrade I had a budget up to £500 and started auditioning various DACs sold at hi-fi shops and retail outlets. None offered a marked improvement over the Pi-DAC. During this time I noted that some used the Burr-Brown DAC chip found in many RPi hats. I now have a Chord 2Qute plus Allo DigiOne; a marked improvement over all I had previously auditioned.
After testing the Ambre for a long night, decided to keep him and stop tinkering with al the separate components.
The advantages of the Ambre against the digione:
I just purchased the Ambre.
I went this way because I have some specific needs for my main listening room - not all rationale, but hey.
Hmm, always wondered whether one could employ one streamer to feed multiple DACs simultaneously. You think this possible?
In my case, I would want to use 2 USB outputs from my Minix Atom to feed 2 DACs and from there into a pre-amp for some A/B DAC listening/testing.
Anyone?
I will certainly find out soon and let you know. I was thinking the use of exclusive mode might mess up switching… but it should be feasible…
I currently run the Ambre with the Onyx (I2S connection) and believe it sounds fantastic.
For the ones, like me, that have both the Ambre and the Digione in competition face 2 face i can tell you that there is no discussion concerning the highest sound performance of the Ambre vs the Digione. If you can not here any difference, the problem is somewhere elese in your system. As usual, we can see the performance of a source when the rest of the system is not a bottleneck.