The moving on thing is just good marketing and I'm as much a sucker for it as any. The 6004 will be a bit more refined but I suspect you'd need to compare side-by-side to really notice.
see if you can get a 6004 on a home trial as for each person here who thinks it is worthwhile, another will say don't bother!
On a general point, the same money on a streamer or DAC might be better looking forwards unless you have a large cd library and have no wish to rip. Or don't have a pc!