Maybe my Excel sheet helps you regarding this
https://www.tonstudio-forum.de/blog/ind … B-MADIfac/

Direct link to the Excel: https://www.tonstudio-forum.de/index.ph … 0-08-xlsx/

What about simply looking at the corresponding HW output where the loopbacked signal originates from ? It is actually the same !

The display of the signal on the HW input is still needed as its possible that you have also incoming audio from the device which is connected to this particular HW input and it can still be routed to another output.

> But also it is even more important to see the Level when another input signal is coming in and probably clip ?

Sorry, I do not get your point.
1. The signal that you loopback to the corresponding input is the output signal, this level you can see at the HW Output.
2. The input signal from a connected device is shown on the HW input and can be routed to any output.
Side note: at the other output you can use loopback it again to record it.
So the analog signal from connected devices is not lost....
Best practise is anyway to use channels for loopback, that are not being used (ADAT, AES, MADI).
Its only a special case that software is so braindamaged to accept audio only from AN1/2 instead of providing all available ports to choose from.

> But it is not only the visibility of the loopback, it is more that the loopback signal is gone out of Totalmix,
> you can't do further routings with loopback, like pingpong from output - loopback - input - routing to
> another output, not possible.

1st of all, the purpose of loopback is to be able to read/record an output signal (submix) without external cables to an HW input. This saves a) cables, b) ports.

Next. No signal ist lost, the audio input of connected devices is being displayed on the HW input.
There it can still be used / routed to another output/submix and if you should need to record this particular one, use loopback again. As I said such trickeries are not required of you use ports for loopback that are otherwise not in use.
For this reason I say its always good to have some ports as a reserve ... either for other connections or ... loopback.

If you need a certain submix on other HW outputs additionally, well then simply provide this submix to these other ports.
TM FX even supports you here by the functions to copy or permanently clone a certain submix.

Whatever I tell you .. final decision is anyway up to RME.

BTW, I only tell you this, because I was not sure, whether you are aware of it, that from functional perspective all is already possible with TotalMix just right now. So .. if you should have a problem to deploy something, that you can solve it now.

a) you can add FX also to the HW outputs
    And if you do not want FX there, well then provide this submix to another unused output, add fx and loopback there

b) this would only be of use for devices with FX so if limited use anyway for a generic TM FX feature

Question is also, whether its worth to add such a switching which makes things not easier maybe even harder to understand for routing deployment and troubleshooting.