Currently testing some more serious lists on friends, and have received some contrasting advice (in particular regarding the Vox Espiritum) regarding something I want to try on an Apothecary.

I play Salamanders, and I'm running a Primaris Apothecary with some flame Aggressors. I want to make that Apothecary my warlord, and then spend 1CP to make him Chief Apothecary. I then want to spend another 1CP on Examplar of the Promethean Creed to give him a second warlord trait. I'd be therefore giving him the following:

Trait 1: Father of the Future (6 for friendly units within 6")
Trait 2: Either Selfless Healer for double heals or Lord of Fire (Re-roll no. of attacks for flamers within 6")
Relic: The Vox Espiritum (Increases aura abilities ranges by 3" up to 9"

Now my questions is essentially whether the relic interacts with the warlord traits to increase their aura to 9". a 9" 6 bubble sounds fun, but one of my friends is pretty confident that the Vox Espiritum only works on auras that are on the datasheet and not on warlord trait auras? I don't see how he's reading the rule that way but maybe I've missed an FAQ/errata or something?

TIA.