The ADI-642 has one headphone output, the device is legacy product and i would choose something new for listening music.

If you can find, get an ADI-2 Pro or ADI-2 DAC

The Madiface has no sound quality, it transmit digital data.
The ADI-642 has only one headphone socket, this is the only part with sound quality, as it is outdated I can't recommend it.

This Streamer N20 cost about 13k, you want best sound quality, the ADI-2 pro is what you want.
ADI-2 Pro FS R
ADI-2/4 Pro
ADI-2 DAC FS

The N20 also has no sound quality at all, it is digital only, not even a headphone output and no analog output.
Can't understand why this should be audiophile, it is just expensive.

No sound quality at all.
No comparison possible.
Either it works or not.
In this case both deliver the same audio quality.

But the devices are different.
The AdI-642 is a digital format converter, the N20 is a digital audio player.

How to measure ? And measure what ?

Digital transmission is lossless and thus does not sound different. The sound comes during D/A conversion.

If you are eager to be able to prove that, get one of the RME reference converters and use the bit test.

For every sample rate, RME prepared a short WAV file, which you can play back with e.g. a music player on your PC.
The reference converter has a detection for this special bit sequence and checks whether the pattern is unmodified.
This way you can validate that the digital path from source (player) up to the DSP of the reference converter is lossless.

For this you have to ensure, to choose a lossless driver and that the volume at the player is set to 100%,
because even a volume change changes the digital pattern.

From my own experience, I can tell you that digital connections like AES, SPDIF, ADAT, MADI are lossless.

For a setup, simply ensure to have the D/A conversion at the very end of the playback path.
All RME reference converters support the bit test, but only the Pro models support AES.
Currently all are sold out, but this appears to be only temporary, so please wait.
Information about the reference converter you can find on the product pages:
https://rme-audio.de/de_adi-2-dac.html
https://rme-audio.de/de_adi-2-pro-fs-be.html
https://rme-audio.de/de_adi-2-4-pro-se.html

See this sticky posting and my blog article for additional information about those devices.
https://forum.rme-audio.de/viewtopic.php?id=32506
https://www.tonstudio-forum.de/blog/Ent … ses-EN-DE/

An alternative is to use an RME recording interface with AES I/O and to integrate the reference converter into the setup.
How such an integration can be achieved, see here in my blog:
https://www.tonstudio-forum.de/blog/Ent … our-Setup/

Do you need this setup only for Hi-Fi use, or do you want to use it for recording, mixing, mastering?

To put an example:

If you do not necessarily need MADI for longer cables (up to 2 km), you can also use such a setup:

PC/Apple
|
| USB2
|
Fireface UCX II [cs]---ADAT OUT----(up to ~15m)----->ADAT IN---ADI-2* [cs] (all models support ADAT I/O)
^
|
| AES (up to ~100m)
|
Player [cm]

cm=clock master, cs=clock slave

In this setup it might be the case that your expensive player can only act as clock master. This is fine.
RME devices like UCX II and ADI-2* are due to SteadyClock FS (tm) technology, the perfect clock slave removing any
clock jitter from a digital connection.
The design of the ADI-2* reference converters is special that even as a clock slave their own FS clock is in use by the circuit for the final D/A conversion.

You could also think of using ADI-2 Pro reference converters in stand-alone operation mode.

Player [cm]---AES OUT--------->AES IN---ADI-2 Pro FS R BE [cs]---AN 1/2---HiFi Amp or active monitors
                                                             or ADI-2/4 Pro SE      \---AN 3/4---headphones
                                                                    /
                                                                   / ADAT/SPDIF(o)
                                                                  /
                                 TV---SPDIF(o)---->4:1 TOSLINK Switcher
                          Blu-ray---SPDIF(o)--/
PC/Record. iface---ADAT or SPDIF(o)-/
                                   Reserve-----/
   
You can connect either active monitors or a HiFi Preamp or pure amplifier; then the ADI-2* would have the role of acting as a preamp. You can even use a TOSLINK switcher to integrate other sources via optical SPDIF, like a TV or Blu-ray player.
Using optical SPDIF gives you galvanic separation  to not get any hum from the TV, which might be connected to satellite TV.

If I recap right you can switch at the reference converter the digital source so that either the player connected through AES becomes clock master or alternatively one of the devices connected to the TOSLINK switcher.

Maybe you can also decouple clock by using the SRC (sample rate converter) feature of ADI-2 Pro FS R BE or ADI-2/4 Pro SE.

If you would tell more about your budget and your demand/use cases for such a setup, then it would be easier to help you with a good setup proposal.