you will need to choose a preamp that has an optical out.
Run an optical cable from the preamp to the jb3. (the jb3 only has an optical input)
Not true in the first case, and not possible in the second.
Preamps are analog devices, they don't have digital outputs. Analog to digital converters (ADCs) provide the digital signal to our recorders. If you're using an outboard ADC with your NJB3, you'll need either:
[1] an ADC which outputs an optical signal
[2] a digital format converter to convert your ADCs coax S/PDIF or AES/EBU signal into an optical signal.
Two good digital format converter options are the Hosa ODL-276 (coax <-> optical converter) and ODL-312 (AES/EBU <-> optical converter)
Alternatively, you can simply use the ADC in your NJB3. In which case, you would need adapters to go from the analog output of your preamp (likely XLR) to the 3.5mm stereo analog input of the NJB3.