Complex rhymes with:
culex, inlex, patlex, proctorsilex, qualex, reflex, rolex, abex, albunex, alpex, ashtec's, avanex, cognex, cortex, culex, dudeck's, forex, gemex, genex, ibex, immunex, index, inlex, koscheck's, micrografx, mondex, moulinex, ovex, pantex, patlex, proctorsilex, purex, quadrex, qualex, quanex, reflex, rolex, rorex, royex, semtex, simex, spinifex, timex, trizec's, uzbeks, vortex
Complex sounds like:
camouflage, campbell's, campbells, cannibalize, cannibals, chambless, chambliss, cineplex, cineplex's, commonplace, compels, compiles, complexes, complies, conable's, convalesce, cosmopulos, cymbals