Would someone explain what "up sampling" means and how it can affect the sound?

I agree with almarg; bombaywalla's post is excellent.

I have to concede that trusting your ears is not enough.  Unless you have ears you can trust.  

 Who are you going to believe, Almarg (and others) or your lying ears?

Ears don’t lie, but do have limitations:

1) you can’t hear something unless you buy it or go hear it somewhere else first

2) If you hear it somewhere else first, you are hearing an entire setup, not just the thing you are interested in hearing. So your ears won’t lie and you know what the thing of interest is capable of sounding like but not what it will sound like back home.

3) Once you buy if you don’t like what you hear then you are back where you started in the first place.

So best to use all information available to help deal with the limitations your ears alone are handed. That helps assure a happy ending sooner and probably avoids wasted funds.

Or just keep trying until....

I think we're getting a bit off topic here.  I agree with what most of you are saying in principle.  I don't think there is anyone who would disagree that the best way to audition any component is in your home system.  But that's not always possible.  When I was purchasing my system, I would bring my CD player to the dealer in order to have some point of reference as to the qualities of the new player compared to what I had.  Speakers are somewhat different in that you never know how they will work in your room, which is why I had a home audition before investing in expensive (for me) speakers.  So I think we all pretty much agree on this.  But what I am saying, and I'm sticking to it, at least for now, is that knowing about the mechanics of upsampling or what DAC chip is not going to matter one iota to whether you will like the player.  I know some people believe that each DAC chip has a sound, or that a ribbon tweeter is automatically brighter than a silk dome and so on.  In my experience, I have found those generalizations not to be true.  But that's me.