Microcontroller PWM to bipolar push-pull amplifier issues. (level shifting)
You can try buffering the output of the filter with a pair of darlington emitter-followers, which will replace the four diodes with four transistors. 







simulate this circuit &ndash; Schematic created using CircuitLab

You can try buffering the output of the filter with a pair of darlington emitter-followers, which will replace the four diodes with four transistors. 

Check that the no-load bias current in the output transistors is not too high. 



It might be easier to use an op-amp though, if you can get some that are suitable.