Can I use the GX90xx module that I already own with the SMARTDAC+ GM?

Yes.
However, note the firmware version that the GM supports.

• I/O module: Firmware version R1.04.01 or later
• I/O expansion module: Firmware version R1.02.01 or later

If your module's firmware is older than the above, you must update it to the latest version by visiting the following URL:
Download page *Log-in Required