Understood. You're controlling the Hub with your HX. The HX seems to be capable of being used as a MIDI controller. I believe you'd be connecting it to the hub via the 5 Pin DIN jacks (though the Hub does have a USB port which you might be able to transmit Midi to the Hub, but it wouldn't act as a host device for individual pedals).
I don't believe the Hub works as a USB host, but it can definitely interface with the One Series including the C4 and Spectrum. In that situation you would connect the C4/Spectrum it to the hub via 1/8" TRRS.
I'm actually curious if the Hub can also pass through direct pc/cc messages to the C4/Spectrum, or if it will only be able to receive Hub scene messages from a controller? The way the Hub is designed, from my understanding, is to store presets which include the bypass state and pc# of a group of pedals. If for example the C4 is on channel 1, spectrum on channel 2, kingmaker on channel 3, and the Hub is channel 4, my understanding is that your ES-8 (or DMC-3XL) will only be able to send messages on channel 4 to the Hub and not pass through Midi messages to channels 1-3 (the individual pedals). But if you create a scene where you just engage C4 with preset #7 (pc#6), then you can save that as scene 1 for example on the Hub and be able to recall that by sending PC#2 to channel 4 (preset 1 to the hub), as opposed to the pedal directly.
Sorry for the word salad haha. @rsmith601 please correct me if I'm wrong.
Someone would have to test, but I'm pretty sure you can have the Hub and C4 on different channels and still control the C4 separately.
This has been stated repeatedly on this thread; there is no C4/Spectrum Hub functionality besides MIDI CC pass thru. Those 2 pedals cannot receive Hub scene messages yet.