If you're using the 5 band passive EQ in the amp block, try cutting the LMid fader by a few dB's. 500Hz is typically found in the low mid freq's on many mixers (those with sweepable mids anyway) and dedicated outboard EQ units. The amp block default EQ is the 8 band variable Q if memory serves. It has a specific 500Hz fader that would likely be more accurate for cutting in the 500Hz range than the 5 band passive. For even greater control, you can add a graphic EQ block, use the 10 band constant Q, then cut the 500Hz freq and adjust the master Q control to effect greater or lesser frequencies around the 500Hz center. The parametric EQ can be used for this as well. Experiment with placing the EQ block before and after the amp block. When cutting frequencies, I've found I like the results better by placing the EQ block after the amp block. For boosting - which I rarely do - placing the EQ before the amp block seems to achieve the desired results for me. YMMV so experiment to find what works best for you.