Guillermo,
on the back of the pro there is a switch which reads "Midi, PC1, PC2, Mic"; maybe you should adjust the setting to Midi or PC1, depending on how your system is set. The manual says how the different settings work.
Good luck.
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.