Cubase not seeing my second interface

I know this is doable because I’ve done it before…but for the life of me…

I have an RME HDSP 9652 with a Fireface 802 hooked up to it. Works fine. (actually have the clocks sync’d now also)
And I want to use by old RME ADI-8 Pro as a second output device for cue mixes, but Cubase isn’t seeing this unit.

Everything seems to be connected correctly and all software up to date.

Any ideas why Cubase isn’t listing this device in the F4 I/O panel?

Cubase only sees the 9652. 24 adat in and out plus spdif. The adi must be connected to adat out of 9652 and audio send to those adats. If you don’t see the adats, they are probably set to optical spdif in the hdsp settings. If set properly hit reset in the input outputs of cubase or restart the computer.
If you don’t succeed ask at the rme forum.

Certainly Because you have the driver of the HDSP selected.
Apart from that the ADI 8 Pro is not an interface at all, it is a standalone AD/DA converter and must be connected as explained by vinark.