[Ari33]

Is it better to risk buying a more bassy earphone such as the Heir 5ai over the Heir 4ai because you can EQ the bass down on the 5ai and suffer from less distortion than you would get vs increasing the bass on the 4ai?
 
Or is my thinking flawed and simply having the EQ even switched on at all.. is the bad thing?

 

[kmhaynes]

It depends on the degree of distortion your source introduces in applying any EQ, in the case of increasing bass.  The JetEffect EQ technology that comes on Cowon players does an amazing job of increasing bass without introducing any perceivable (at least to me) distortion (I use some for my Ety ER4P).  I would say the same about most head/earphone amplifiers -- many provide a bass boost that is clean.
 
My personal preference is to have a clean, neutral sound that does not artificially over-enhance bass -- that seems to be the best audio approach to me.