Source patching audio "light" will not turn on
Your guess is correct. If you have an audio asset active into the Source Panel, you can't activate the Source Patching for an audio track that does not match the type of the asset. Premiere seperates between Standard (Stereo), Mono, 5.1 and Adaptive. You can tell the track type by the corresponding icons in the timeline: 



From Top to Bottom: Standard (no Icon), 5.1, Adaptive, Mono.

You can't put Multichannel audio (where multi means more than two) in Stereo tracks and vice versa. Instead, you need to create new tracks of the matching type. To do this, right-click on any audio track1 and select Add Tracks… from the context-menu. This opens a pop-up menu where you can chose to add any number of Audio and Video Tracks. Make sure to select the right Track Type (in your case, you'll need 5.1 or Adaptive). You can also delete the superfluous Audio Tracks from the same context menu (accessed via right-click).

Note that this will not change the Audio Master Type. When creating a sequence, you can change this in the Tracks tab, as well as control how many audio tracks of which types are added.



1 Note that you have to right-click in the right area, as there are several available context-menues hidden in the timeline, depending on where you click. To access the context-menu described above, you need to click anywhere between the Sync Lock icon (to the right of the Track Targeting toggle) and the column containing the Track Type icons (to the left of the timeline itself). You can also access this via the menu over Sequence → Add Tracks….