[jamesino]

I find the treble on my HD 650 to be a little underwhelming. If I choose to boost the treble by a notch or two on Foobar2000, how much quality loss will i expect in other areas? 

 

[smedley]

    Why would you lose anything?  You use the equalizer to make them sound the way you like it to sound , that's what equalizers are for.

 

[jamesino]

Will certain frequencies be clipped? Even though I find the treble recessed, would boosting it up a bit cut off some other parts of the frequency range?

 

[emertxe]

You should rather decrease db of the rest (bass+mids) than increase treble to be completely safe as far as clipping is considered. As for digital EQing, I find it imperfecr as it introduce certain jitter, making SQ suffer (it makes music sound a bit blurred). You should also consider the fact that each headphone responds differently to EQing - some very well across the whole frequency spectrum, some not.
 
I would rather use analog-based EQing... But if you really need to EQ using your computer, pay attention to what kind of equalizer you use - I do very like Nugen SEQ1, PLParEQ, apQualizr and especially Brainworx digital v2. If you want something that's free, try EasyQ or Electri-Q.