1) Firewire back to back
This won't work: PC---USB---UCX----FW400----Presonus Firepod
You need a FireWire controller and ASIO driver to communicate with the Presonus Firepod.
It is not possible "back to back" between UCX and the Firepod.
2) Using ASIO4ALL can't be recommended
PC--"ASIO---RME ASIO Driver---------USB-------UCX
\--4ALL"---Presonus FW Driver-----FW400---Presonus
Nobody recommends it in a professional/semi-professional environment.
Me neither, I only want to mention it for completeness of the case.
The bad thing is that it adds another ASIO protocol on top of the RME and Presonus original ASIO drivers.
Then the DAW has no direct access via the real ASIO drivers to the hardware anymore.
But this is the "key" of using ASIO drivers for direct access to the hardware to get stability and low latency.
Moreover, the compiled-in RTL values in the ASIO drivers for AD and DA would not fit anymore, so that latency correction in the DAW will most likely be wrong.
3) The only possibility to connect UCX and Presonus, but with strong limitations (2 ch)
These two devices use different drivers, but you can only load one audio driver into the DAW.
This means you would need to make the UCX as your main interface (to have TotalMix FX as main mixer)
and to connect the Firepod via a digital port.
Sadly, the Firepod has no support for ADAT, it supports only coax. SPDIF, which is a 2ch protocol.
I leave it up to you whether only 2 channels are worth it to connect the Presonus Firepod via SPDIF(c).
4) The only valid solution, get a new preamp
The only solution that makes sense is to purchase a new preamp and to connect it via ADAT to the UCX.
I would recommend a RME preamp, but I assume you want an inexpensive solution.
Best solution would be to add a Behringer ADA8200 as preamp / AD/DA converter to the UCX via ADAT, see here:
PC---USB---UCX---ADAT OUT--------------->ADAT IN---ADA8200
\---ADAT IN<----------------ADAT OUT---/
Clock master Clock slave via ADAT IN
(set jumpers on the back accordingly)
https://www.thomann.de/de/behringer_ada … ragain.htm €198
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13