I have found the suitable EQ settings - which resemble the 'Beats' sound in Poweramp - on another forum and I'm going to post them here:
The finder of this has used an older version of Poweramp but you could enter these settings into the newest one. The author has also enabled Dolby surround in his Desire HD. So we can't fully imitate the Beats audio since our Wildfire S doesn't support Dolby, but this is the closest we have come so far. I have tested about 10 different songs with my HTC connected to my Kenwood stereo and I have to say the original 'Beats' sound is still a tiny bit deeper and more direct (Stock player vs. Poweramp; I have flashed the latest patch provided by einstein.frat). Nevertheless you must really listen for a difference to notice one.
One last thing: disable the 'Limit' option in Poweramp's EQ and set the 'Bass' and 'Treble' knobs as shown. Actually you could play with them a little bit, but don't exceed the 1/2 mark (the position of the knob's mark pointing upwards). You could leave the 'Tone' setting on, it doesn't really matter.