@VegetarianNachos
Your 2019 iMac should have an excellent screen in it, and it's worth using good quality parts for the conversion.
1. "
Single cable from Mac supporting 5k/60/10 output"
Any of the available boards can do this, using DisplayPort or USB-C where available.
Except JRY-W9CUHD-AA1 and R9A18 - these are 8 bit only (with a single cable for the R9A18).
10 bits using an HDMI input requires a board with HDMI 2.1, which is limited to JRY-W9RQUHD-FA1/SA1,the T19, and the upgraded R1811 HDMI 2.1 version.
2.
"Making use of the internal stereo speakers"
All boards have an onboard amplifier chip, with the JRY boards having the lower power available (2-3 watts) and the better specified R1811/R9A18 (10-15 watts), which allows better volume control from the Mac's keyboard.
3.
"Using iMac power button to power Monitor"
4.
"Using existing AC power connector on iMac"
This is easily done with soldered connections.
"I am looking at using the JRY-W9RQUHD-SA1..."
The JRY--SA1 gives an excellent picture quality using USB-C/DP. HDMI is probably OK, but not enough users have reported on this, and the board's firmware doesn't allow is operational mode to be checked.
It's audio power output is similar to many low-mid price monitors on sale.
Better audio most likely requires more audio power.
"Do you think the iMac power supply with a DC to DC converter would be more trouble than just buying a 24V supply and wiring up the AC plug and iMac power button?"
The iMac internal PSU is quite noisy at the low power output that a DIY conversion requires.
If you want to use a 12V to 24V converter, then
@SubDriver also considered doing that in his excellent
SA1 conversion.
"Would the R1811 V4 with the HDMI 2.1 ports be a better card to use? (I have yet to find one of these available to purchase)."
The R1811 HDMI 2.1 version is only available from StoneTaskin on their own .com website, or maybe their affiliate AliExpress pages?
There are three advantages to using this board, in addition to its better audio:
It has an IR remote control, so it's easier to adjust its settings.
It has more fully developed DDC-compliant firmware, meaning it can be controlled from the Mac's keyboard.
The JRY boards only have partial (brightness only?) compliance.
And the latest firmware gives much more information on its operational settings.
There seem to be three versions of the R1811 being sold:
The original R1811 V4 was first sold after 2019, and now comes with V04 firmware.
The cheaper boards sold on AliExpress seem to be this generation.
In late 2023 the R1811 V4 HDMI 2.1 version became available, but it's availability seems to be restricted to the principle vendor.
It comes with much more advanced RealTek firmware, and there also seem to be HDMI 2.0 versions using this firmware, but the price of these newer HDMI 2.0 boards (but still labelled R1811 V4) is higher than older boards, and they seem to be only available from the same vendor as the HDMI 2.1 version.
Good luck with your planning and build. 👍
