ADAT is a standard digital I/O port, you can choose what you want.
As the FF400 has only 1 ADAT port, you are limited to:
- 8ch @single speed (44.1/48 kHz)
- 4ch @double speed (88.2/96 kHz)
Recording at quad speed is really not required.
When choosing a preamp you may want to check several things
- how it integrates into TM FX, best integration with Octamic XTC (from used market) as Auxdevice, then you can store most important preamp settings directly into TM FX snapshots/workspaces
- gain range, modern preamp designs support up to 75 dB gain range, I think 60-65 dB is a good minimum value to look for 1st
- level stability of the inputs
- special features like pad, instr inputs, phones add outputs, operateable at the front
- USB Class compliant mode (Octamic XTC), to be able to connect it as preamp/interface to iPAD or Windows
- the usual things like SNR, etc ...
- amaount and type of digital and analog inputs
- whether it has analog output as cue out port or whether its possible to route audio from ADAT input (if present) to analog outputs
- features like format conversion between ADAT, AES, MADI (Octamic XTC).
The most versatile product is IMHO the Octamic XTC (currently only available from used market).
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14