Using two RME Ucx

I have 2 RME FF800's - you can definitely record on multiple channels with these. I also group them together as an Aggregate Device under Audio Midi Setup (in Utilities).

If they have internal power supplies I would personally not use an aggregate device, but it may work for you.

I would run a Lightpipe cable from ADAT out on unit A, to ADAT in on unit B.

Unit-B is the only USB connection to the computer. UNIT A wil be the master clock OUT, Unit B will slaved to the digital clock of Unit-A. Unit-A shouldn't need any adjustments. Use Total mix or the hardware to set things up, or use the hardware to set Unit-B to slave to incoming ADAT clock.. this should give you 8 extra inputs at either 44/1 or 48kHz, 24-bit.

It's actually much simpler than my description. You only need one ADAT optical cable,

re: Internal Power Supply

Because two identical USB Bus powered devices will have clock issues. One of them needs an external power supply.

RME Software is usually solid. The setup I describe should get him extra input channels as long as the device furthest from the computer (Unit-A) is the clock master.

Hi, is this the RME Interface that has both USB and Firewire connectivity? 18 channel input ADAT connectors?

I can tell you how to do it, these have external power supply correct?

Curious about your response, specifically the internal power supply issue. I have also done/do what you suggest regarding light pipe. It makes monitoring on two FF800's possible.