I have the S400 mkII driven by a Cambridge Audio power amp and Anthem STR preamp. I've got mine placed about 12-18 inches from the wall, which gives me a satisfying boost in the bass area. I don't honestly hear a night and day difference with them placed 6 inches from the wall either, although more is better.
One thing about these is that they do incredibly well with DSP if you want to adjust the tone. In my room they had a dip at around 1200 Hz and it robbed the treble of some presence and detail, DSP'd that right out and now the treble performance is shockingly close to my Kef LS50s (and everything else is much better).