HDSPe MADI FX and 9652 are using different ASIO drivers, so DAW/applications can only access the one or the other as they can only load one audio driver at a time.

For what purpose do you need the 9652 if you have the HDSPe MADI FX?
Do you have analog expansion boards for it and want to make use of the analog channels? (*)
If not then leave the 9652 out of your system, it doesn't bring you any real benefit.
You should have enough ADAT channels by the ADI 648.

(*) If this is the case you could install the driver of the 9652 and route analog channels through ADAT.
As you have the ADI-648 you could connect 9652 to there via ADAT.
By this you could make those analog channels available to the main card (HDSPe MADI FX) through ADAT (ADI 648).

Clock synchronization can be provided by ADAT if you also connect a TOSLINK cable (ADAT) from ADI-648 to 9652.
In the settings dialog of HDSPe MADI FX configure it as clock master (clock source = "internal).
In the settings dialog of HDSPe 9652      configure it as clock slave   (clock source = "ADAT...").

But you also need to pay attention to some more things:

1. whether your PC is capable of handling so many channels. HDSPe MADI FX has 390 channels and each of the HDSPe 9652 has additional 26 channels.
2. whether your PCs case offers enough vertical space to add the amount of needed slots for the PCIe cards itself, their daughter boards and additionally room for any potential analog I/O cards for the 9652.

I personally would not add this complexity.

Stay with one HDSPe MADI FX, connect everything additional through MADI.

Theoretically .. the fewer cards in the system, the lesser amount of interrupts and context switches need to be handled by the CPU of your system. This results in fewer DPC calls and the DPC latency of your system should be a little lower. By this the system stays more agile/stable to process audio in time even at lower ASIO buffersizes.

Tip: the HDSPe MADI FX has a special driver with an optimization to only allocate driver resources (-> CPU load) for active channels in groups of 8 ports. How exactly this is being counted I can't tell. Maybe MADI1 IN 1-8, 9-15, etc ... So you could save a little CPU load by keeping active channels as close to each other as possible. Not sure how much this will save, maybe only a little, but if you can organize things in such a way, then do, maybe it saves a few CPU cycles, DPC latency (inside of your PC, not round trip lateny regarding audio/monitorin).

This is mainly a forum for RME products. My general advice is to get Windows 11 compatible components but to use Windows 10 for the time being. Windows 11 is too new and I have a certain doubts that Windows 11 is in a state to be ideal for recording and any DAW product.
I would get two SSDs for your system, one main installation of Windows 10 Pro which you use for your DAW work.
And the 2nd one for a parallel deployment of Windows 11 to be able to keep track of it and to make comparisons.

Esp. if audio should be your business you need a stable / tested DAW system. I would contact companies that offer turnkey systems for audio. Then you are on the safe side and do not loose time with any potential issues. But I can't tell you which company in australia offers such systems / services, you need to google or ask in forums.