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Hey there, hope anyone can help, I'm pretty frustrated, because I cannot get my 16 inputs setup with two 8PRE USB to work.

General information:
- Win 8.1
- Driver Version 4.0.5.9198 (reverted from 4.0.5.9644, cause I thought it might solve the problem)
- Primary Motu connected via USB, Optical Input set to "ADAT", Master Clock Source set to "ADAT Optical", Sample Rate 96k
- Secondary Motu connected via two optical cables to primary Motu (secondary Motu's top and bottom row out --> primary Motu's top and bottom row in), Clock 96k
- both units set to type II mode

Everything syncs up nicely, I can play audio through primary motu's main outs and headphones, great.
But there is a huge problem with CueMix FX:

If I feed any signal to secondary motu's analog input 1 it appears both on ADAT 1 and ADAT 5, the same for ADAT 2 and 6, 3 and 7, 4 and 8. That means that by only using 4 analog inputs (1 - 4) on my secondary motu, all 8 ADATs on my primary motu are occupied. If I feed any signal to analog inputs 5 - 8 on my secondary motu, CueMix simply shows nothing on the respective ADATs. (Because they are occupied by carrying copies of analog inputs 1 - 4)

Screenshot:
http://i.imgur.com/jLo1udQ.png

Why is the one-to-one mapping not working? I mean it definitely should be like:

secondary motu's analog input 1 -> primary motu's ADAT 1
secondary motu's analog input 2 -> primary motu's ADAT 2
.
.
.

secondary motu's analog input 8 -> primary motu's ADAT 8

Anyone who encountered the same problem?
Would be great if anyone could help.

Assuming the USB version of the 8-Pre works in the same way as the FW version which I have...

If you're running 96kHz as you say, that higher sampling rate needs to use 2 ADAT channels for each input. Hence your problem.

The "solution" is to drop 96kHz to 48kHz, when all 8 ADAT channels will be available.

I need to contradict. Originally ADAT was designed to transmit in maximum 8 channels with 24Bit/48kHz per ADAT cable. With the so called S-MUX mode it is possible to double the sample rate to 24Bit/96kHz but then only half the number of channels, which is 4 then, can be transmitted. For that reason the 8Pres (FireWire AND USB) have two banks of optical connections, in order to transmit channels 1 - 4 in 96kHz over cable 1 and channels 5 - 8 in 96kHz over cable 2.
I don't know if I understood you right, but thats nothing new, thats what they are advertising everywhere.

“The 8pre as your primary audio interface

Use the included CueMix™ software to mix all 16 inputs from your computer. Eight channels of ADAT optical I/O make the 8pre an ideal companion for a digital mixer. Two ADAT lightpipe connections work together to support a full 8 channels of optical digital I/O at any sample rate up to 96kHz.” (http://www.motu.com/products/motuaudio/8pre)

I highly recommend everyone having that problem to create a TechLink on the Motu homepage. The issue is known to the Tech-Support and they are able to solve it.

Best

Great! It works! What's the fix?
And also, does this happen with OSX as well?

Motu Tech-Support told me to treat it as confidential, so all I can say is, if you encounter that problem create a TechLink on Motu homepage and the guys will fix it (they are fast, lasted one or two days only). Sorry cannot say any more.

For the lazy folks: you can simply copy my failure description from above when creating the TechLink, so its less than 1min of work.

Yes, the problem is independent on the OS.

i bought the 8pre yesterday and i have exactly the same problem! i fiddled around for 12 hours and now i found this post which makes me relaxed again...
...i hope they contact me soon...