Sure you could run through a head unit. That's the easy way to go. Just stash it somewhere. (As long as the head unit allows hand control of the iPad/iPod).
iPhone 6 Plus (iTunes library/iTunes radio/Waze, etc) to Airport Express via AirPlay. Toslink out of Airport Express to Helix P-Six DSP. PHD AF 1.C tweeters, PHD FB 4.1 midranges. Jehnert Door Cards and mid-bass'.