Hey there, you definitely can control the BeatBuddy through the MIDI Maestro using an expression pedal, but you would need the MIDI Maestro, the BeatBuddy does not have a pedal input.
The Aeros will change tempos when the BeatBuddy changes, but it is not made to change after something has been recorded to a song, the Aeros must record and playback in the same tempo.
So
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Yes, you can use an expression pedal to control the BeatBuddy, and the BeatBuddy will control the Aeros but I wouldn’t try to switch tempos on the Aeros except before recording.
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If you have the MIDI Maestro, you can use the BeatBuddy the foot switch pedal and an expression pedal all at the same time, yes.