High performance stereo and mono-block amplifiers.  Stereo amplifiers are an excellent way to keep space requirements down while providing large quantities of clean power for larger dynamic speakers.  Mono-block amplifiers separate the left and right channels into two separate units which provides greater power and cleaner sound because left to right crosstalk is reduced.  An additional benefit of mono-blocks is the ability to place them adjacent to speakers, allowing very short speaker cables.

Amplifiers come in two primary types:  tube and solid state.  Tube amplifiers tend to be much lower power per dollar but give a sense of harmonics and life-like textures to music.   Solid state amplifiers have more power per dollar and provide much greater dynamics and soundstage size, and generally have lower noise floors.  As each amplifier type increases in cost and performance, they actually tend to gain each other's benefits while ameliorating their respective weaknesses.