I would second Nezer's opinion.
I've got the 4s and a Corda amp used with a not notable, old JVC carousel CD player. I can compare to 4s's directly out of a Radio Shack pcdp with high--for these days--output. The point is that my sources are not exceptional in any way and probably qualify as "mid-fi" on the most generous estimate.
The with-amplifier experience is preferable, certainly, but by such a small margin that I use whichever combination is the most convenient for me, and, more often than not, that's without amplifier. Of course, my pcdp is not underpowered for the purpose. But the less-than-enviable status of both my disc players could be preventing my hearing what the amplifier can do in a higher level system.
So, if money for audio is tight for you, I recommend working first on getting a source that is sufficiently clean and powerful. If you're already OK in those respects and have amplifier power to spare built in to your source, get the mr. fixup converter cable or the soon-to-be-introduced Etymotic one that converts your P to an S so that it gets a little smoother. Lastly, get a nice amplifier. Nice as an amp can be, it probably will contribute less than any of the other elements.
Never yet have I heard an amp take anything to a whole new level. Of course, my sect in the audiophile faith tends to put transducers on the altar rather than other components. There are a number of different faiths among us, and you never know which is yours until you've made a few experiments.
