I use 4.1 speakers atm.. and its already great.
I mean.. in BF2 and 2142 for example, you can hear wither someone is lefr or richt behind you, so you're turned towards him much faster.
as for more speakers than 7.1 i doubt it... there wouldnt really be a market for that.. i mean, have you seen the prices of a good/midrange 7.1 speaker set? immagine when it goes further.. noone would really buy it anymore I think.. or at least not enough to justify the expenses for the company.
further,.. the placement of the speakers would also stop those thest from selling.. i mean who of you all can say thay could fir in 8 speakers, and a subwoofer, on the place where they would be supposed to be easely?