How to monitor live intensity levels using OSC?

Have look to the EOS manual "Implicit OSC Output". Every time you change the value you get a message from EOS like:
OSC              2024-11-06 10:07:31.447 [10.101.1.201:57834] SEND [OSC Packet] /eos/out/active/wheel/1, Intens  [0](s), 1(i), 0.400(f)

You can also subscribe parameters, e.g. "/eos/subscribe/param/pan"

Have a look to the #lighthack example on https://github.com/ETCLabs/lighthack/blob/master/box_1/box_1_src/box_1_src.ino

Have look to the EOS manual "Implicit OSC Output". Every time you change the value you get a message from EOS like:
OSC              2024-11-06 10:07:31.447 [10.101.1.201:57834] SEND [OSC Packet] /eos/out/active/wheel/1, Intens  [0](s), 1(i), 0.400(f)

You can also subscribe parameters, e.g. "/eos/subscribe/param/pan"

Have a look to the #lighthack example on https://github.com/ETCLabs/lighthack/blob/master/box_1/box_1_src/box_1_src.ino

Yeah - but I believe this is only for the selected channel - not for all channels

With /eos/out/get/patch/<channel number>/<part number>/list/<list index>/<list count> (Page 664)
you should also get the current level which you see also in Patch on the console.
As an alternative you can parse the sACN output.