how much difference does a player make

Can make or break your system. Second most important piece (next to speakers)in the audio chain.

Have a friend bring over a high end player or get your audio store to let you have a demo. You will be stunned at the difference a good CD player can make.

"Would I actually hear a difference?"

It depends on your system. You need to let us know what the rest of the system is.

My guess is that if the HT setup cost much under $5000 then the difference will not be pronounced. If it cost under $2000 I doubt you'll hear any difference at all.

The reason I say this is I used to own a Mission Cyrus 2 amp and Cyrus speakers .... great stuff, but mid-level. It would be a $1000 amp and $500 speakers at today's prices. I couldn't hear any difference between a cheap Yamaha CD player and a Meridian 506.20 in that system. That same system could clearly resolve the difference between a $250 turntable and a $1000 turntable, indicating to me that the "source first" argument of hifi is not so applicable with digital playback.

Fast forward, and I now have a more transparent amp and speakers, but the difference between an inexpensive DVD player and a $1000 stand alone player is subtle. It may be worthwhile, but it definitely will not make your "jaw hit the floor" as some others would have you believe.

Another option: Add a killer DAC for the two channel audio portion. Works for me.

Agreed with MDhoover. . .used a high quality DAC for years with a variety of players and always experienced an improvement over the players' analog outputs. Still use one for my sony cd changer, iPod, and Airport wireless.