How to connect a 3 phase motor to class-d audio amplifiers
Possible solutions:-


Convert the push-pull outputs to single-ended using audio transformers. This requires 3 relative bulky transformers that might not be easy to source.
Split the motor's Delta connection into 3 independent windings. Each winding can then be connected to both output terminals of an amplifier channel. If your motor has its winding wires brought directly out to the plugs then this is relatively easy to do. Simply unsolder the plugs and separate the wire strands. Then use an ohmmeter or continuity tester to find which phase the other end of each strand goes to (there may be several strands per winding). Install 6 plugs and you're done!





Connect each motor phase to one output terminal of each amplifier channel (leaving the other terminal disconnected). This should work with class D amps such as the TDA7489, which produce differential PWM (both terminals produce a similar PWM waveform, but one is the antiphase of the other). What you are then doing is using one side of the amp's bridge output. 


Whatever method you use, you still have the problem of getting the rotor to stay in sync with the driving frequency. If the motor is lightly loaded and you change frequency slowly then the rotor may be able to keep up. Otherwise you need some way to detect the rotor position (eg. Hall sensors) and adjust the frequency and phase to match it. Remember that a BLDC motor is synchronous, so it will not run with the rotor slipping behind like an induction motor does.