I also have some Apple TV problems using HP 8300's with Ivy Bridge i5-3470 with a
HD2500 graphics IGPU, and either an Nvidia Kepler GT 730 or AMD RX 560 video card
as a DGPU.
I can't make the GT730 work with Apple TV at all.
With the RX 560 machines, I must turn off the Intel IGPU in BiOS to get Apple TV to work.
And even then, I am not able to view content stored as HLS Video, such as Snoopy in Space,
but only from downloaded content which is stored as an MPEG-4 movie in m4v format. I
cannot stream any content, but must first find content which can be downloaded, download
it, and wait for the downloading process to finish post-processing.
I've tried invoking various shikigva options, and various shiki-ids as described in An Idiot's Guide to
Lilu and its Plugins, to no avail. However, Ivy Bridge systems are known to have DRM problems,
and your Intel graphics may work better than mine.
If you have another working machine, you might consider downloading content to it and testing
from there. Set your working System Preferences / Sharing to turn on Home Sharing of Media Sharing.
You should be able to access downloaded content on the working machine from your other machines
on the home network. I have a working (real) Mac Mini, and it allows me to check whether there are
problems in the downloading process or in the playback process with my hackintoshes.