Thank you for your detailed feedback.
Yes I can confirm that delay on the last two channels on the 8 channels groups, it happens due to the A/D converters. (CH 7-8; 15-16; 23-24)
If your application is sample accuracy, there’s two solutions for you.
1. As you can count on constant delay on those channels, you can compensate that with post processing.
2. Use digital input instead of analog. There are 3 option cards available for the device: ADAT