If the OpenVox card is supported by Linux drivers, there there is a chance it will work with the Linux version of 3CX. However...even if there are drivers, it may (probably) still not be "officially" supported by 3CX, which would mean no auto-provisioning.
You mention FXS, is the OpenVox FXS ports (ATA), or FXO (a gateway?). You may need to clarify.