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What to do with a mixed model setup?
If a mixed setup is created (one-way models mixed with multi-way models) the master should be a multiway model. Since a mixed configuration has conflicting inputs (digital vs high-level), the one-way models are muted if a digital source is selected at the master. If this is undesirable, consider a two-way model in BTL or dual mono as subwoofer amplifier.
https://www.hypex.nl/FAQ-Hypex/Fusion-Amp-Family/What-to-do-with-a-mixed-model-setup