OP, I'm a bit confused about what you're seeking. I don't own the same display you have, but I do own the same Sony headphones and I have no issues with them. You're not sharing everything about your configuration - wanting to connect the display via HDMI and you also have the headphone processor connected via HDMI. You do know that the processor has an HDMI switchgear built in, but it needs to be configured properly, although that's not likely your "problem".
Your Mac has one HDMI signal to output to an HDMI device - if you've connected the processor via HDMI, that's it. DisplayPort includes HDMI, but if you've connected the Sony processor via HDMI you've essentially terminated the single HDMI signal there's nothing to output to your display. I looked up your display, and it has mDP and DP ports - so either you're not using a mDP or DP cable to the display or you've not related that you have other devices in your "chain", and I'm not going to speculate further about this.
I'll offer what I have going on. I work in 4 locations, and use either the Sony headphones or a pair of Grado SR325e cans, and I bring both with me when I hit the road - the Sony's for movies and the Grados for music, and when I get tired of wires I'll connect the Sony headset. But, I use the headphone jack for both - did you know that the headphone jack on your rMBP also has an optical signal?
I connect my Sony processor to the headphone jack on my late-2013 rMBP's headphone jack using an optical cable, and it works perfectly, with a tweak. The Audio Preference Pane needs to be adjusted - it supports up to a 192 kHz sample rate for audio playback when using the Toslink optical digital out port. To enable playback via Toslink, select "192000.0 Hz under the "Format" pop-up menu in Audio MIDI Setup.
Also, and don't laugh, when on the road I use a newer Airport Express and its optical out port. A friend of mine made fun of my AE, but I swapped it out for his Schiit Bifrost (a $350 DAC) and he didn't notice for the entire weekend - until I told him. Apple's Airport Express is pretty sweet, and includes a powerful DAC. Before you judge, read Ken Rockwell's breakdown of the latest Express's output (and comparison to a $3000 CD player, using 10-year-old dollars) -
http://www.kenrockwell.com/apple/airport-express-audio-quality-2014.htm - he's got lots of graphical data and readout in that post.
On the road, I'll connect my Sony processor to the Express's optical out and use Airplay during playback of my movies and some music - I'm pretty anal about my sound quality, and it's surprisingly good. This, coming from a longtime Grado and non-Chinese-made Sony headphone owner. And, I own a Bifrost DAC too...
I know that the optical output is 5.1 and the Sony's have a virtual 9.1 output - but, that's the point, it's virtual. I, personally, can't tell the difference between virtualized 5.1 and 7.1 and 9.1 when the source material is encoded properly (I use Apple Lossless for my good stuff). Consider using the optical options you have available, and ditch the HDMI for the Sony processor and you'll free up a port for other uses.
