Hi,
Soundcraft and DiGiCo use different pinouts for their Cat5 madi-connections. Look those up and you should be able to make an adapter cable.
Only difference between Madi BNC and Madi Cat5 is that BNC is 75 Ohm asymmetric and Cat5 is 110 Ohm balanced twisted pair.
DiGiCo Solutions little red/blue boxes convert between the two. A Neutrik AES/EBU passive impedance transfo in each direction should do as well.
With some DIY research you should be able to achieve your goals.
Good luck,
Best Rogy