well it's kind of odd, i was reading some stuff about 9230 and remembered that i'm using a asrock C2550D4I board and that one has 4 port marvell e9230, thing is running fine with dsm 6.1 so it cant be a driver problem
if we rule out power and cable it might be a combination of controller bios and driver?
i found something about adding "iommu=soft" to grub config, can't hurt to try and its easy to do/reverse
just edit the grub.cfg on the first partition of the usb flash drive
set extra_args_3615=''
->
set extra_args_3615='iommu=soft'
in the end the easiest way will be to look what 4port sata card worked for other people owning a gen8 and use this
as long as we don't use a newer kernel i dint think there is a solution when it depends on the driver, as i said, the ahci driver is part of the dsm kernel and the way dsm is "hacked" we can't exchange the kernel (at least so one did that so far)
also overthink whats features you need, omv has plugins too and as its a full linux some stuff is much easier to achieve then with the dsm appliance, dsm/xpenology ,is limited in some areas and will cost a lot of time to make it work in a way you need it, even applying updates can be a problem, if it comes to invested time i'm not so sure that dsm will save you anything, you will just have to invest time in other areas then you would with omv