In a DRM scenario, there would be an audio equivalent to HDCP in place, so you'd need a piece of technology which it's illegal to clone and only available if you sign a restrictive licensing agreement.
Mind you, you'd still be able to cannibalise an existing set for this.
Given how "successful" HDCP has been, I'd give it a month or two of survivablity. And yeah, as you mentioned, anyone with basic electronics skills (or for that matter, could follow a youtube video) could simply mod their hardware to plug whatever they want in.