I own a pair of Infinity Sigma.
They are outstanding. I had several opportunities to listen high end speakers in international HiFi exhibitions and the Sigma are certainly among the top.
However like any high end speaker they need excellent material to drive them. Multi amplification with high speed amplifiers, excellent and digital pre-amplifier, top of the line cabling and connections and excellent reproducers like CD and DVD players.
The sound of the Sigma is very realistic, almost absent distortion, deep and very clean bass.
My speakers are driven by 2 double amplifiers of 250 Watt per channel for mid and tweeters and 315 watt per channel for the woofers.
The sound is so clear and sharp that you don't have the feeling you are at almost max power until you try to speak and you cannot listen to your own voice.
The only disadvantage, if we say it is a disadvantage, the quality of sound given by the Sigma is such that if a CD is not well recorded, all defects are clarly evident. Like microphone badly placed among an orchestra, bad mixing/level of instruments, singer with bad quality microphone. Fortunately these defects are more present in older CD's where recording and mixing was analogue.