Just a few ideas.

1. Attenuate means to reduce, not boost as i think you meant?

2. Remove the frequencies you dont want rather than attempting to boost those you do.

3. Lower the other parts in volume

4. Look at your other parts to see if there is something interfering in the same part of the frequency domain

5. Reduce the rez on your filters, no doubt this is reducing available headroom and is certainly distorting the frequencies you wanted to leave clean.

6. Also why cant you properly accomplish this with EQ? which eq are you using? Hope it is a quality one.

7. what sort of quality is the sample you are using? HQ?

if i get any more ideas ill write em down.