The AD-8000 has two basic modes of operation - SOURCE and DESTINATION mode.In SOURCE mode, everything is as it seems. That is, whatever source is selected in the SOURCE SELECT matrix will be sent to the analog and digital outputs (also indicated in the matrix). For digital inputs (including all AMBus inputs), select DIGITAL IN on the desired channels, select the desired digital source (AES/EBU, S/PDIF, or AMBus A, B, C, or D) in the SOURCE SELECT routing matrix, then select the desired master clock under SYNC SOURCE. Again, note that in SOURCE mode, DIGITAL IN must be selected to play back tracks from Pro Tools or any AMBus source.DESTINATION mode is quite different. Analog or non-AMBus digital signals entering the AD-8000 are routed to the main processor (for UV22, meters, etc.) then routed to the selected AMBus card destination. Select the desired AMBus destination by holding down the STEREO SELECT button and then pushing the headphone volume control until the letter (A, B, C, or D) of the desired AMBus card appears in the seven segment window near the headphone output. So, for example, in a Pro Tools system, analog inputs appear on the meters (and UV22'd if desired), are routed to the Digi8 AMBus card (AMBus A), returned into the same AMBus card, then routed to the analog and digital outputs. This is like a "tape monitoring mode" or "confidence monitoring" mode on tape recorders. It is the "set it and forget it" mode when using the AD-8000 with Pro Tools. This mode most closely resembles the operation mode of the 888 and 888|24 (with some differences detailed below).Note that in DEST mode, the meters only monitor the initial non-AMBus inputs (the source), NOT the return levels from Pro Tools. So when you play back your Pro Tools tracks after recording, you will not see the meters working on the AD-8000 -- this is normal. When Apogee first designed this feature, we asked many Pro Tools users whether they preferred to monitor the input or return signal on the meters while in DEST mode. Overwhelmingly, the answer was that they wanted the meters to monitor the signal that was being recorded to disk because, they felt, it is then when it is important to have high quality metering and 'over' indication.To recap:In SOURCE mode, whatever source is selected in SOURCE SELECT takes over the output bus. In DEST mode, the selected AMBus card (shown in the seven-segment display window near the headphone output) takes over the output bus and all non-AMBus signals are routed directly to that AMBus card.