The only reason I mucked with the common.bank file is because at first, every time I used the RELATIVE_TO code to assign it to an object, it played the ambience located in that common soundbank therefore I changed it (regrettably).
I've made a new soundbank with 5 different events, linked the bank and GUIDs under [SOUNBANK_0], copied the relevant code from the GUIDs and pasted it beside the ID. It worked in game but like I said earlier it's limited to a very small area.
When I got it working on the assigned objects (with the ambience sound from common.bank), you could hear it while you were inside of the object and the sound only went away once you left the object. The object I had assigned it to was quite large (larger than those spheres in the vid) so it's got me thinking I could make a large object covering a large portion of the track so that the ambience sound is played in the background.
The other problem I encountered was I made about 20 events and position them close to one another so that the sound was continuous when you left one event and entered another but every time you entered the next event, it restarted the sound. So I scrapped that idea.
This post I found had a marching band seems to be played over a large area so according to this it must be possible. Unless it's a volume thing where it's turned up high?