I found a C541i on the 'gon for $275 and bought it last month. It's a good CDP for the money. I have to say, that previously I owned a NAD C521BEE CD player for all of one week. I bought the BEE used for $175 from the classifieds here and when it arrived I was thrilled with the sound. So thrilled in fact that I decided to sell it on Ebay and upgrade to a C541i that showed up in the classifieds here a couple of days later.
The C521BEE sold easily on Ebay (for more than I paid for it) and the C541i is a good but subtle upgrade to the BEE. The C521BEE is an oft overlooked good deal CDP (lots for the money like the C320BEE integrated Amp)
The C541i has a bit more air around instruments, the ability to play HDCD (which it does very well, I think) and possibly a bit tighter bass response.
I haven't heard the C542. But I have heard two opinions: 1) that it's a very small subtle improvement and 2) that it's a huge improvement that has to be heard. I have no idea which of these is true.