I did direct radiating speakers for my side surrounds and in-wall bi-pole for the back surrounds with good results. I put the in-walls about 56" apart since my seating is about 18" from the back wall. Each driver pair ( 1" & 6.5" ) are canted at 15° from the center line. Produces a pretty wide back surround field which might not work as well with direct-radiating speakers up front. My back surrounds are Definitive Technology UIW BPZ/A.
Denon AVR X7200WA, Emotiva XPR-5, Emotiva XPA-7, Sony XBR 75" 850C, Oppo BDP-103D, Roku 4.
DefTech BP7000SC (L/R), CLR3000 (C), SM55 (FH), UIW BPZ/A (SB), UIW 75 (TM).
JBL L7 (Sur), EoSone RSR 350 (RH).
PC 2.1 setup. Emotiva Stealth 6, SVS SB2000 sub, Emotiva DC-1 DAC.