2019 5K Retina iMac External Monitor DaisyChain Issues...

I'm starting to ramp up my Day Trading, and, thus, need more visual Real-Estate than just my iMac in order to keep everything straight.


have a 2019 5K Retina iMac.

It has 2 x T3, and 4 x USB 3.0 ports....NO Display Port.

I have 3, identical, ASUS ProArts PA278CV monitors that will allow DaisyChaining via DisplayPort Cables.

I got a USB-C --> DisplayPort Female Dongle Adapter for one of the T3 ports on my iMac.


Here is my (semi-functional) current set up:

iMac

⬇️

(USB-C --> DisplayPort Female Dongle Adapter) -- (DisplayPort Cable)

⬇️

ASUS #1

⬇️

Display Port Cable

⬇️

ASUS #2

⬇️

Display Port Cable

⬇️

ASUS #3



ASUS #1 is working as it should (ie: acting as an external monitor...I can drag from my iMac desktop to ASUS #1, and it is not a mirror image of my iMac, but a separate screen / Desktop).


ASUS #2 & #3 are working, in terms of powering up, and getting video feed from ASUS #2....HOWEVER, they are both MIRRORING ASUS #1, and that defeats the whole purpose of having monitors 3 & 4, if they aren't going to be independent of one another.


As you can see, from the ASUS manual, these ASUS monitor have no issue being DaisyChained, as long as the connection from the monitors is via DisplayPort Cable, and not USB-C.




However, when this wasn't working as expected (ie: the 3 external ASUS Monitors being independent of each other), I started doing some Internet sleuthing, and came across this AI answer:



I also noticed that when I went to my iMac's "Settings", that it would recognize the FIRST ASUS External Monitor, but NOT the other 2 behind it:



So:

  1. Am I understanding correctly, that I can only have 2 external monitors coming off of my iMac...AND...I have to sacrifice BOTH of my T3 ports to do it?
  2. If so, what kind of stupid design flaw is that (as if we don't have any other externals that might need to use one of those ports)?
  3. Is there ANY workaround so that I can have 3 external (independent) monitors coming off of my iMac (maybe a USB-C to a hub with 3-DisplayPort Outs)?


Any and all help, suggestions would be greatly appreciated.


Thanks,


-J

iMac 27″, macOS 15.3

Posted on Mar 24, 2025 6:25 PM

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5 replies
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Mar 25, 2025 8:01 AM in response to jman995

1) That is correct.

2) It is not a design flaw. It is a Hardware Limitation.

3) A TB/USB-C dock would give you more ports, but still only 1 Extended External Display on that port.


If you what to run 3, 4 or 5 displays in Extended Desktop Mode..?

Then consider upgrading to one of the Mac Studios models.

Identify your Mac Studio model - Apple Support

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Mar 25, 2025 8:03 PM in response to jman995

You're welcome.


The latest Mac mini supports 3 external displays.

see "Display Support" at > Mac mini (2024) - Tech Specs - Apple Support


The Mac Studio supports 5 to 8 displays depending on the model.

see "Display Support" at > Mac Studio (2025) - Tech Specs - Apple Support


I didn't mention the Mac mini because it only supports 3 external displays.

Which is the same number of displays as your iMac's display and two external displays.

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Mar 26, 2025 12:05 PM in response to jman995

Your USB-C (Thunderbolt) ports support both Thunderbolt and DisplayPort Alt Mode.


Your iMac can support two external 4K displays or one external 5K display. It does NOT support three external displays. It also does NOT support DisplayPort MST daisy-chaining. It would support attaching two external misplays (4K or lower resolution) through one dock, but only if that dock was a Thunderbolt dock, not a plain USB-C one. (And this would not make it possible to attach a third external display.)


iMac (Retina 5K, 27-inch, 2019) - Technical Specifications - Apple Support

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Mar 25, 2025 4:48 PM in response to den.thed

Thanks for the reply, explanation and link.


A few more questions:

  1. Just to be clear, I'd have to get a "Studio" (a "Mini" wouldn't work?.....I'd ONLY be using the Studio or Mini to be able to pull up a browser window (Chrome or Safari), and run 3 independent / extended monitors off of it to be able to keep track of the markets...so, no heavy lifting like Video Editing or Gaming...just powering / watching 3 independent / extended monitors).
  2. If I do wind up getting a Mac Studio (or Mini, depending on your answer to the previous question)....do I have to sacrifice one port (ie: T3/4/5 or HDMI), PER extended monitor, or can I DaisyChain?


Thanks,


-J

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2019 5K Retina iMac External Monitor DaisyChain Issues...

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