My understanding of MADI is ...

It's a bus with up to 64 channels which you can assign / map per device as you want, with the technical possibility of multiple readers or writers for each of the 64 channel.

So you could ie cable one or more Madiface Pro into a MADI bus to have ie backup recording or to share preamp or converter resources between two or more DAWS.

Normally you would perhaps use devices with more madi busses or use the features of a MADI router, but I think this way you can even use more devices on one MADI bus than you have free audio channels.

It should perhaps be clarified with RME upfront in which cases you need to be careful not to get maybe unwanted offsets because at least on recording devices I see no parameter like auto ça compensation.

Also interesting to know is whether there are a few samples offset when powering off a madi device in a chain or not. If the device is powered off then it can't participate in auto ca detection to automatically compensate offsets on a madi bus...

I think you mean at 88.2/96 kHz ..
Then you have 32 channels in an out.

If you want to use both devices :

Inputs and Outputs
- map Ferrofish 1..24 to madi 1..24
- map XTC 1..8 to madi 25-32

OR

Inputs and Outputs
- map Ferrofish 1..32 to madi 1..32
- map XTC 1..8 to madi 25-32

and do not use Ferro 25-32 if you want to use XTC or power off ferro ....