Bingo!
I am still very happy with my RME Raydat PCIe solution. I don’t know if you can actually use the MR816x as standalone ADAT converters. If this is possible it would be a good idea to keep the AD/DA converter part of it.
On my personal journey through pro audio land I have not yet seen an external interface that is as reliable as the RME PCIe solutions, that also offer the lowest latencies in the native part of the industry. I have not yet worked with thunderbolt solutions, though.