I can do some testing but yes, it can send both PC and CC messages. Is it going to be the only thing in your midi chain? Is it going to be on the floor or in a rack?
My setup would be GCP Midi OUT > GCX Midi In > GCX Midi out > H9 Midi in. I will probably keep the H9 on the same midi channel as the GCX for simplicity but I may move it to it's own channel.
The trick is to know what CC's and PC you want to send. For instance… If you want to control TAP, you are going to want to set a particular CC on the GCP button you want to use for TAP, then set the H9 to learn and hit that button.
The GCP can control several different midi devices at one time and you can name them. I have mine setup for 4 "presets" and 8 "Instant Access". So the top left button on my GCP is set to TAP and it sends the CC that the H9 responds to, it's momentary so you click it in time with the music to set the tempo.
The 4 preset buttons are setup to call the GCX loops I wish to engage as well as send the right PC down to the H9 to select the preset I want. There are bank up/down buttons on the GCP that allow for more presets. The presets can be named.
The only thing I am not sure about is if the H9 can send tuner info back to the GCP, I doubt it can.
I have not setup my expression controllers to the H9, but as an example, I used one of my controllers to adjust the global input level on my GMajor2 to work as a volume pedal, the other one I setup to control the mix of my filter patches.
Here's a video that explains how to setup the "learn" function on the H9 to accept the CC for TAP. (lets hope it works)