First off. Thank you to everyone who has replied so far.
I've got power and cases and such. I actually have a 18 port external duplicator case that I used for an older version of this.
This newer version is 20 slimline drives mounted paired in a rack chassis with 10 5.25 bays. I've got a dedicated 850 watt power supply on this case with a loopback cable so when I turn the power on at the switch it turns right on.
First I tried what worked on my last version of this (15x full height dvd drives) which was 3 sata port multipliers hooked to 3 of these
USB3.1/3.0 To ESATA (6Gb) Adapter,JMicron Chipset Port Multiplier, eS3U31 | eBay which worked beautifully for years.
The new one I tried 4 multipliers and 4 of those adapters which kept dropping out, when turned out to be the bd-rom drives higher data rates were blinking the adapters.
I then put in a motherboard that handled port multiplication and removed the usb step and it sees all the drives, but if any 1 drive has a read error that set of 5 will cycle as a group and you have to restart 5 reads.
Then I tried these
https://www.amazon.com/dp/B09KDLKYRN?psc=1&ref=ppx_yo2ov_dt_b_product_details
Which ran into a similar issue.
Then I tried two of these Glotrends SA3112J. But I think these run as a multiplier as well.
My next attempt will be 20 of those sata to usb adaptors, but I'm going to run 1 drive to an adapter, and then each adapter gets a dedicated slot on a StarTech pexusb3s44v since that card has a dedicated usb controller for EACH port on the card and doesn't share the line.
If that bombs I was going to try an older AsRock X99 Extreme11 board since it has 18 sata ports already. But I'm trying to avoid just building a whole computer for just this since I've got a PowerEdge R720 that can handle this work in the background already if I can get this addon set built for it. I've also got an R920 that I'm rebuilding for my students AI work that I can lean into as well if needed
Based on the recommendations so far:
The IBM ServeRAID suggestion. - I've got LSI9211 cards that didn't work, but I'll hunt down a 9207 as well and give it a try.
In that case you may want to look at JMB585 PCIe cards with around 5 ports. - I've tried the JMB575 but I'll try this as well thank you.
Keep them coming if anyone else has ideas. I'll source parts this weekend and report back on what does and doesn't work.