Thanks for putting your question up here Diabolo.
In order for multiple A to D units (such as your D8s and the 828) to function together, they must share a common digital clock. The Digimax D8 has only two ports that can carry a clock signal, its ADAT Out and Wordclock ports. Here is your manual:
https://pae-web.presonusmusic.com/downl ... ual_EN.pdf
From that manual:
• Clock. This button sets the DigiMax D8 to External digital sync or sets the Internal sample rate.
o Press the Clock button once to set the clock to internal sync and your sample rate to 44.1 kHz. This will make the DigiMax D8 the Master clock of your system. It will be sending out word clock via the ADAT output.
o Press the Clock button twice to set the clock to internal sync and your sample rate to 48 kHz.
o Press the Clock button three times to set the clock to external sync. This will make the DigiMax D8 look for a master clock via the BNC word clock input. Your sample rate will automatically change to match that of your master clock.
Please note: If you are using the DigiMax D8 to record into a DAW application like Logic, ProTools, Cubase or Sonar, you must set the sample rate inside your host application to match the sample rate you set on your master clock generator.
If you were just going use a single D8 with your 828, all you would need to do is connect the D8 ADAT Out to an ADAT In port on the 828 with an optical cable, select your preferred sample rate on the D8 (44.1k or 48k Internal) and slave the 828's Clock to the ADAT port to which the D8 is connected.
If you wish to work with only a single D8, you already have everything you need; refer to your 828 manual to learn how to properly set the 828 Clock source to External.
However, you have TWO D8s, which complicates things somewhat. To slave more than a single D8 to your 828, you will need to use the Word Clock ports on all three devices. Your 828 will be the Master Clock. The procedure is explained in detail on page 14 of the D8 manual:
3.3.2 Using multiple DigiMax D8 with the FireStudio LightPipe
To clock more than one DigiMax D8 to the same external sync you will need a BNC T-Connector for each DigiMax D8 you are connecting to your system. This is called parallel clock distribution and will allow word clock to be sent to and relayed from each DigiMax D8 in the chain. The last device in the chain will need to have a BNC terminator attached to the other side of the T-connection. All the devices between the master clock and the last device in the chain are un-terminated so as not to load the signal down.
Please refer to your manual for the cables and connectors you will need.
Once you get the proper Word Clock gear, you should be able to get this sorted quickly.