"Re: 10.9.3 with late 2013 MacPro D700s
Just a note that I have three displays: an Apple LED Cinema Display (24"), a Planar 27" PXL2790MW hooked up via Thunderbolt to Display Port, and a Seiki 39" UHD TV (via HDMI). All work fine after the update - nothing has shut off. (I asked how he updated - via SU, or D/L updater (delta or combo)) - I did the updater from Software Update. I can also run HIDPI scaled mode on the 4K screen now
I tested Final Cut Pro X as well. All seems fine (I just did some simple work), but noticed the following:
FCPX on the late 2013 mac pro or 15" Retina MBP supports broadcast monitoring (HD, and 4K) via HDMI right out of the computer - in "A/V Output" mode the HDMI panel will show up if turned on. It won't however work with Final Cut Pro X to monitor in 4K UNLESS you turn the HiDPI "retina" scaling off first (in 10.9.3; under 10.9.2 there was no option). That's easy enough to do and is a quick click of a button in display preferences. In fact FCPX won't show any video out on the panel in A/V Output unless the monitor is shown at its native resolution.
This is a little annoying, but not a huge deal. (I mostly monitor 1080P, so I use an AJA T-Tap for that. That way I keep the 4K set at scaled to "retina" for general computing and using FCPX monitor 1080 off the AJA box on a different HDMI input. That way I can have the best of both worlds... a retina computer screen for watching 4K videos, retina websites, etc, and monitoring in 1080 with FCPX. But if I want to monitor 4K while editing, I have to switch the panel back to native resolution... which looks great in FCPX but makes anything else look tiny. Same goes if I want to use A/V output with any resolution if I didn't have a T-Tap; the 4K panel must not be set to scaling in OSX.
I thought that might be useful info; especially for those who might not even realize they could playout at 4K 24/30 out of HDMI on 3rd screen while editing in FCPX with two other screens on a late 2013 Mac Pro or 15" Retina Macbook Pro.
On Premiere Pro CC you need a 4K playout box for unadulterated broadcast monitoring, OR you can simply move your viewer window up there. It will play in 4K in either scaled or native panel resolution. But that will be your program window, not a separate broadcast style monitoring with no UI elements. You can still use 3 screens in "retina" mode by splitting up the windows between the three screen with the 4K panel being HIDPI/Retina.
Thanks for the positive report, a nice change as there were many posts in Apple's forums on problems with multiple displays after OS X 10.9.3 update. (I linked to some early OS X 10.9.3/external display problem posts Thursday night, including posts that only 2 of 3 (or 4) displays worked after installing the OS X 10.9.3 update.)