The 8pre as an optical converter
The 8pre is two products in one: a FireWire audio interface and an 8-channel analog-to-digital converter.
When the 8pre is not connected to a computer via a Firewire cable, the front panel "Mode" LED changes from "Interface" to "Converter". In this mode, the 8pre acts as an 8-channel analog-to-digital converter that can add 8 mic inputs to another ADAT optical-equipped audio interface, digital mixer or other device.
For example, if you already own an 828, 896 or Traveler interface, you can connect the 8pre to the optical bank on your MOTU interface to seamlessly integrate the 8pre's additional eight mic inputs into your MOTU interface CueMix mixer or host software mixer.
When operating in this mode, the 8pre simply routes each mic input signal to the corresponding optical output channel (mic input 1 goes to optical output 1, etc.) When connected to a MOTU host interface, such as the 828mkII shown above, these eight optical input signals are then routed directly into the host interface's optical bank, so they appear side by side with all other inputs in the host interface's CueMix Console, as demonstrated below, which shows the 828mkII CueMix Console with the eight optical inputs (the eight faders furthest to the right) renamed according to the mics, instruments and other sources connected to the 8pre mic inputs:
This approach has benefits over simply connecting the 8pre as a second Firewire audio interface. For example, it conserves Firewire bus bandwidth (for other devices, such as hard drives). It also streamlines your workflow by avoiding the extra setup procedures, software settings and performance issues often encountered when operating multiple Firewire interfaces connected to your computer. By connecting the 8pre optically to another Firewire interface, it becomes, in essence, a seamless extension of the other interface.
The 8pre has the ability to support 8 channels of optical output at 88.2 or 96 kHz (the 2x sample rates). This means it can be connected to another device that also supports 2x optical sample rates (via two sets of optical connectors) to add all eight mic inputs at 88.2 or 96 kHz. A perfect example is the 2408mk3, which provides three optical banks that can operate at 96 kHz. By connecting both optical banks from the 8pre to two optical banks on the 2408mk3, you add eight 96 kHz mic inputs. And they can be mixed as a seamless extension of the 2408mk3.