I have my pa500 (bought it in 2008) and my psr s900 side by side. I connected the pa500 into the mic line with gain control set at maximun position. The psr is connected into a regular line in at half the volume (otherwise the sound is overloaded). This way I get similar volume in both units. The pa500 sounds clear and crispy. No problem.

The flufle valve is adjusted, and the blue leds are on. My be it needs some oil replacement to get higher volume.