You can disable ports visibility for TM FX in the channel layout …
See "Hide channel in mixer / matrix" there ...

I mentioned this before—this applies (only) to TM FX.

At higher sample rates (double- or quad-speed), audio data is multiplexed across two/four physical channels.
All physical channels are still utilized by this.
The useable number of channels shrinks to 50% (@double speed) or 25% (@quad speed) on each MADI bus.
This means you have access to 32 ch @double speed) or 16 ch @quad speed per MADI bus.
But still, all 64 channels are in use on each MADI physically.
Only logically, you have a decreased number of channels.

Therefore, MADI Bus 1 still starts at channel 1 and MADI Bus 2 needs to start at channel 65.
At double speed, you have to access channels 1–32 and 64–96, rather than 1…32 and 33-64.
At quad speed, you have to access channels 1–16 and 64–80, rather than 1…32.
I am not sure whether it is easily possible to organize this differently.

Maybe RME can give you more inside on this topic whether this is possible to change.

So you want to configure this in the driver for every sample rate, even single speed,
even if the physical channels that are not allocated to devices, could be used for loopback?

I doubt that this will come, but wish you good luck with your request.

I remember that only the FireWire driver had an option to disable digital ports on the card.
Most likely, the intention was, to lower the needed bandwidth over FireWire if there were issues handling more channels.

So if I summarize this correctly, it should be possible in the driver, to select
- the channels that you want to use and
- the mapping of the channels to numbers, in what order they should be presented to the application

This regardless of the sample rate, even for single speed. But a little warning here regarding single speed.
The user might want to use the free channels on each MADI bus for submixes and loopback recording purposes...

Of course, you can daisy-chain multiple devices on a MADI bus.
Up to 8 Octamic XTC (8x4 Mic channels) or even another recording interface to be able to access those audio channels.

The only thing you should be aware of is, that
1. You will get 3 samples latency per MADI device on one MADI bus. This is little, but I want to mention it.
2. When working at double-speed, you can only work with one of the two Ferrofish A32, as then you have only 32 of 64 channels available due to port multiplexing.

You didn't mention that you only use single speed, and I thought the reason for getting the HDSPe MADI FX is, to have two MADI buses available, so that each of your Ferrofish converters can work at single or double speed as needed.

You can even have 3x Ferrofish A32 by using the 3rd MADI bus of the HDSPe MADI FX. If you buy the optional OPTO-X module, then this can even be optical, which is nice for galvanic isolation and even longer cable runs up to 2 km.

See also my blog article to the HDSPe MADI FX, where I mention all this:
https://www.tonstudio-forum.de/blog/Ent … Pro-FS-BE/