Every band that adds an oud discovers the same problem in the first rehearsal: it disappears.

Make room rather than turning it up

Amplifying a quiet instrument into a busy mix produces feedback and a thin, brittle tone. The better approach is arrangement. Have the guitar play higher or lower, thin out the keyboard voicings in the middle register, and give the oud passages where the texture opens rather than passages where it competes.

• The oud is at its best in the gaps — an answer to a vocal line rather than a bed underneath it.
• Doubling it with anything in the same octave wastes it. Two instruments in that register sound like one blurred instrument.
• Live, a good contact pickup blended with a microphone beats either alone, but the microphone should carry the character.

The instrument was developed for rooms where it was the loudest thing present. Respecting that in the arrangement is more effective than fighting it at the mixing desk.