External monitor reporting no signal despite detection in xrandr

Question

I've installed Arch and xfce4 on my Macbook Pro retina 10,1 (2012). I'm trying to set it up with my Asus PB278Q external monitor.
When I run xrandr, I get this output:
Screen 0: minimum 8 x 8, current 4800 x 1800, maximum 16384 x 16384
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-0 connected 1920x1080+2880+0 (normal left inverted right x axis y axis) 600mm x 340mm
1920x1080 60.00*+ 59.94 50.00 29.97 25.00 23.97 60.00 50.04
1680x1050 59.95
1440x900 59.89
1280x1024 75.02 60.02
1280x960 60.00
1280x800 59.81
1280x720 60.00 59.94 50.00
1152x864 75.00
1024x768 75.03 70.07 60.00
800x600 75.00 72.19 60.32 56.25
720x576 50.00
720x480 59.94
640x480 75.00 59.94 59.93
480x576 50.00
480x480 59.94
DP-2 connected primary 2880x1800+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
2880x1800 59.99*+
DP-3 disconnected (normal left inverted right x axis y axis)
DP-4 disconnected (normal left inverted right x axis y axis)
So the external monitor is being detected by HDMI-0, but my external monitor is reporting no signal (and yes input is set to HDMI on the monitor). Also strange that xrandr is reporting it as 1080p but it's actually 1440p.
The wiki on multihead tells me to use the xrandr command along these lines:
xrandr --output HDMI-0 --auto --right-of DP-2
And this does move the external screen around, as in my mouse can move off my laptop screen where I've positioned the external screen, but there's no signal.
My graphics card is GeForce GT 650M; I have the nvidia package installed. I tried looking this up, but I couldn't find anyone talking about the monitor being detected in xrandr but there being no signal back to the monitor. Also in the xfce display settings, it has grayed out the option to mirror the displays, not sure if it's that indicative of whatever I'm missing.

Answer 1

I have some new information. I tested it on a Viewsonic 1080p monitor I had with a VGA-to-Thunderbolt adapter. This worked perfectly straight away. So I tried the same connection for the Asus monitor and it too worked perfectly.
So I know I'm lacking something with HDMI. I'd still like to solve this because the VGA connection is capping my resolution at 1080p.
$ lspci | grep VGA
01:00.0 VGA compatible controller: NVIDIA Corporation GK107M [GeForce GT 650M Mac Edition] (rev a1)
$ lspci | grep HDMI
01:00.1 Audio: NVIDIA Corporation GK107 HDMI Audio Controller (rev a1)
Am I missing some sort of HDMI compatible controller for my graphics card? I installed the nvidia package as the wiki tells me to do, and I'm not sure what else is needed.