Hi Alex and waedi,
I would do it the other way around and make the more advanced interface (802) to the main interface. Both is possible, but after reading this you will agree, that you have more advantages this way.
A few steps:
Recommendation: connect the 802 to your computer, best via USB, then you can also perform firmware updates through USB which is not possible with Firewire.
1. 802: In the driver settings dialog perform the following settings
2. Connect 802 "ADAT2 OUT" to Babyface "ADAT IN" using a TOSLINK cable.
I can recommend Mutec cables: https://www.thomann.de/de/mutec_optisches_kabel_1m.htm).
3. Do not connect USB so that the device is in stand-alone mode, see also manual ch 31.2
(https://www.rme-audio.de/download/bface_e.pdf):
In stand-alone mode, the unit operates as AD- and DA-converter. Analog inputs are routed to the digital outputs, digital inputs to the analog output (that's what you need).
When receiving a digital input signal in SPDIF format, it will sync itself on the external sample rate, from 32 kHz to 192 kHz.
Advantages:
the 802 is the more advanced interface with better technical specs
you can also use the other channels of the 802 (Mic inputs, phones, ADAT I/O)
you can use higher clock rates up to quad speed (192 kHz) without loosing channels. In your proposal to connect the 802 through ADAT to the BBF you can only use single speed up to 48 kHz to be able to transfer the 8 analog channels.
the 802 will learn the sample rate from the application and the BBF automatically through SPDIF
Option1: get an ARC USB if you want a remote control for the TM FX control room, to be connected to an USB port on PC.
Option2: use an ADI-2 FS instead of the Babyface, more modern converters with better specs, then you can either sell Babyface or use it for other / mobile purposes.
Not 100% sure because I do not own a 802.. Another thing to consider might be with which setup the 802 starts in stand-alone mode, if no ARC (the old Advanced Remote Control, which is not available anymore on market) is connected.
According to the manual you can store settings in each of the 6 profiles, but its not fully clear whether one of those will be loaded per default duriing startup of the device.
It would be a little "add-on work" having to send the proper MIDI command after each power cycle, to restore the settings of one of the six profiles. This also requires stand-alone MIDI control to be enabled, see manual ch 28.6, which can have certain side effects. According to manual: Note: When not needed the stand-alone MIDI operation should not be active, as the unit will react on MIDI notes after power-on, and will also send MIDI notes.
This is an additional reason, why I would prefer to use the 802 as primary device, assuming the assumptions are correct.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14