Could you elaborate on the connection scheme of your setup? Are the
different Motu boxes connected via the AVB switches?

The Motu boxes are connected through a Motu AVB switch and AVB streams. As I do not have OpenAVB working (yet), the connections to and from Linux are done through USB2. In all cases the main control machine is connected to a 16A and auxiliary computers through the 24ai (because of AVB stream count). Everything else connects through the internal routing matrix and AVB streams, very flexible. All devices slave to one over AVB. Input and output not to the computer are handled through analog and/or ADAT I/O.

As the channel count is high 64 channels is a must - I had discarded the Motu devices because they were limited to 24 channels I/O but then they issued a firmware update that enabled a configurable tradeof between max sampling rate and number of channels over USB2. I was looking at a solution using MADI before, but this was more flexible and cheaper (limited budgets), but of course very vendor specific. I have (currently) three use cases for this setup, one is using this as the core I/O for the GRAIL, our "portable" 3D surround speaker concert system - tested in two concerts so far. Another is for the control system of an ongoing upgrade for our concert hall (the Stage) from 16.8 to 48.8 (this is the one that forced me to find a solution). I'm also testing this to replace the existing audio I/O for our Listening Room (just testing this last Friday, looks like may be able to run this at 64x2 instead of the current 128x2 with RME and MADI / RayDAT cards).

So far so good... hopefully I will not run into any pitfalls :-)