Why do music players sound different?

[TheExodu5]

Preface: I am a graduated computer engineer and work in the software business. I am also a relative newbie with respect to the audiophile scene. That being said, my father is an avid audiophile and I have had the pleasure of auditioning many setups with him. Recently, I built him a music server and we've auditioned the Meitner, Invicta, and Weiss DAC202 on his B&W 800 Diamond speakers.

 

I should have rather phrased the question: Why should music players sound different?

 

While auditioning, I did not detect any difference in between Foobar, Media Monkey, and JRiver. My father says he could. Furthermore, I did detect a difference in between optical and USB...USB was more focused, and optical was a bit more diffuse, and I suspect that is due to the added jitter of optical.

 

I'm not going to discount the possibility of there being differences...as I have said I am not an experienced audiophile and I was listening to material that I wasn't overly familiar with, so differences might be hard to pick up. However, I am perplexed as to why there might be differences.

 

So, back to my question, why should players sound different? Does anyone here understand the inner workings of this software? As far as I'm aware, the process should look something like this (assuming no DSPs are used):

 

Software reads WAV -> Software converts to PCM -> Output over an interface using that interface's driver API

 

Where is the subjectivity in this chain? To me, it can only be when the WAV is converted to PCM. How does this conversion occur? Is it done using a custom implementation? Is it done using a standard software library?

 

I'm not particularly interested in answers like "well they sound different to me, so they must be different". I'm interested in the why. I would be very interested if someone with some technical understanding of the subject could chime in.