I think it's more a matter of OS and functionality.
Under MacOS aggregation of devices is a standard feature of the Apple MacOS / it's audio infrastructure.
Under Windows there are two options:
a) aggregation of same or different interfaces supported by the same ASIO driver
b) aggregation of devices with different types of drivers, even ASIO and non-ASIO, by using a 3rd party tool: ASIO4ALL.
Option b) has the disadvantage to create a non-standard / not supported setup, because ASIO4ALL is an additional driver layer on top of the real hardware drivers. By this the application has not the direct access to the HW, all has to go through ASIO4ALL at first.
Operational aspects:
When using multiple recording interfaces in parallel you have one TotalMix FX instance per recording interface, where you can't route channels across TM FX boundaries.
For pure recording this is no big issue as the DAW can access all channels of up to three or more (not officially tested by RME) recording interfaces.
But if you want to route audio from one to another recording interface then you have always the latency over USB/FW and you need to route in the DAW.
This can "partially" be solved by using ADAT ports for connections between the recording interfaces, which you can also use for clock synchronisation (instead of using word clock).
But .. ADAT has here a certain limitation. A maximum of 8 channels is supported at single speed (44.1/48 kHz. Even less at higher sample rates (4ch@double, 2ch@quad speed).
And .. maybe you need those ports more urgently for connecting external devices such as preamps or converters.
So .. there are tradeoffs to be made.
In contrast to use several interfaces in parallel with some tradeoffs you have the alternative to use a MADI-, AVB- or Dante-based setup. Ok the prices might be higher but you have a few clear advantages:
- full TM FX routing capabilities
- more headroom for future expansions
- longer cable lengths compared to TOSLINK
While we are at it, in such a multi-recording-Interface setup, all interfaces need to be clock synchronized. Under Windows you need to configure the same ASIO buffersize in the driver settings for all connected devices supported by this driver.
It should best be the same type of interfaces to have the same converter latency to avoid offsets between recorded tracks.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14