i auditioned at length both the sophia2 and w/p8.
i would agree with jfrech's comments. the sophia2 is more forgiving than the w/p8 with mating and synergy issues upstream. i found the sophia2 had a more even-handed top to btm coherence and shines with small ensemble performance that doesnt require nuance and tactile umph at the extremes. the sophia2 is an LF speaker, but at its bottom, it presents with speed and clarity. however, IMO, it is clearly no match at the bottom end for the w/p8. similarly, the top end of the w/p8 excels over the sophia2 with acoustic instrumentals (i dont listen to electronic music, so i have no opinion there) though the wp8 requires MUCH greater care in set up and component synergy. i found the wp8 gave an overall larger tactile and "live" experience, speed, nuance, finesse etc, but i, like many, am caught in the realization that you indeed need the entire system to be of high caliber with wp8s (i am not there yet).
re: amps - i recently spoke to pass labs about the new xa-pt5 series, they suggest the xa100.5 to fully realize the potential of the wp8, though i imagine in a small room, less class A wpc is workable. i would assume the xa30.5 is more suited to the sophia2 which is easier to drive than the wp8. i fully agree with tomer that the arc ref110 is not sufficient to control the w/p8. my x350.5 exhibited much greater command.
perhaps you will have to weigh your patience with a 2-3 year upgrade path if you go with the wp8s because you will be living with speakers that may show off a variety of ills in your present system until all moves up to the wp8s level.
the sophia2s + purchasing higher quality components+cables this year will net a wonderful system to live with now.
depending on the overall budget in a 1-3 year time frame, for $40-50g total (just a $ range from the air) you can certainly assemble an excellent coherent system with sophia2s, but a system with potential frustrations if the wp8 were in a system of the same size budget.
other: the room size should not be the issue. the wp8s will not sound like their hands are tied behind their backs in a small room. they present superbly at low volume levels, IMO better than the sophia2 for the reasons i mention above, provided the wp8 are part of a system helps them realize their potential. cheers.