None of the dlc is showing up in the downloaded content menu? Any ideas?

Did you check under the "Installed Content" tab? It's easy to miss.

I've been having the same issue with 3 attempts at installing the game. I downloaded and installed all using Galaxy, (most recently with 1.1.12).

I checked all 3 tabs in the game's start screen for DLC and all were empty. "Other Campaigns" is greyed out.

I'm thinking it may be because I saw an "Invalid Command Line Switch" error after entering the admin password to allow it to install DirectX SDK.

I did try to verify, but when it went to install the above, I'd get the same error again and no DLC appearing in the list when I got ingame.

I did not have any other version of Dragon Age on my computer at time of install, but may have previously had one that I deleted (since it is in my Origins Library). I don't think I ever installed the Origins version of DA:O though.

I used the GoG downloader links, and set to NOT automatically install, so I could install later (I started the download and left).

Worked perfect for me. I got 22GB of setup/install files.

After I installed it, All the DLC was installed and activated. I didn't even see an option to NOT install/activate it.

Does Galaxy force an install from the internet, or can you set it to just give you the files, to install later?

Galaxy can either install directly, or be used to download the installers to let you install games yourself. I told Galaxy to download the installers overnight, so later tonight or tomorrow I will try the manual installation.

Edit: As I found in another thread, running the game with Admin permissions shows all the DLC.
Edit 2: This works even better, no need to run as Admin: https://www.gog.com/forum/dragon_age_origins_ultimate_edition/i_cant_see_any_dlc_or_the_other_campaigns_is_this_game_fully_drm_free/post9