The S4i utilizing the same great technology of the S4b enabling a DPC array and timbre matching not only in the raw materials but in the critical frequency response, power response, phase, and in addition THX Dominus surround certified.  Able to blend seamlessly into any home theater as a stereo pair with a subwoofer, center, or surrounds to the be the most useful model in the lineup for small, medium, or large home theaters.