As I think I have said before we have a “three of everything” (where everything is speakers, amps and cable looms) policy in the demo room. Three manufacturers gives us 95% coverage of our distributor base and always allows us to present dCS components in a familiar system context. Bear in mind that from a distributor’s perspective lines they don’t carry are “the competition” whereas from ours they are just “other manufacturers”.
It also helps that for this same reason they are the components that our products tend to be presented with at shows so we know them and the people that supply them well, know how to set them up quickly and get the best out of them, and whom to call for help if we run into problems.
But there is no runic significance in these choices. They are not the only choices, just a small subset of the possible choices that we happen to be very familiar with.