Hello, Quad cortex is more than a guitar processor, it is a studio processor, it requires microphone preamps to optimize its use in the studio.
these are some suggestions:
- Universal Audio 610
- Tube-Tech MP-1A/MP-2A
- Neve 1073
- Chandler TG2-500
- Avalon VT-737
- Grace Design m101
- SSL Alpha VHD