Read as many pages as you can from about here...
In short... ST is slightly better than the STX.
But whether the diff. is worth it, depends on your usage scenario.
i.e. Is PCI acceptable for you build etc.
Re amps, not sure how it compares to other top-notch external amps.
I believe it's "okay", but as always, you'll prolly have better discrete ones.
IIRC there's some discussion about that in here too.
Otherwise just start a dedicated thread, someone will know.
Edited by jalyst - 8/15/11 at 12:08pm