Forget about "ubuntu audio plugins", I understand this was an error. I'm sorry!
I seem to have a hard time explaining myself so if you watch this:
and jump to 2:14 it might become clear.
Here he is adding linuxsampler as a midi instrument within ardour3. In the video you can see that there are a number of other instruments he might have added when he created the midi track but he chose linuxsampler.
The proper name of the thing I need? I need to add midi instruments to midi tracks in ardour3 either via plugins or immediately when creating the midi track.
For example, as in the video, add linuxsampler upon creation of the midi track.