Historically, most acousmatic works were composed in stereo and performed, or “diffused”, over loudspeaker orchestras. These systems furnished performers and composers with a wealth of opportunities to enhance the spatial contrast, motion, and musical articulations latent in the music. Although loudspeaker orchestras, stereo diffusion, and—more recently—hybrid performance techniques remain alive, especially in Europe, there is a trend towards fixed installation, high-density loudspeaker arrays (HDLAs), which I will call permanent HDLAs to differentiate them from loudspeaker-orchestra HDLAs. Permanent HDLAs (P-HDLAs) stimulate alternative approaches to musical space and pose challenges in both spatial composition and performance, encompassing both technology and aesthetics. This article consolidates many of the technical and aesthetic approaches that I have found specific to P-HDLAs with an emphasis on the application of higher-order Ambisonics (HOA) at fourth-order 3-D and above—what I will call V-HOA (“very high-order” Ambisonics) as distinguished from lower orders, or L-HOA (lower than fourth-order HOA). These approaches are guided by spatial-audio research, and then developed in a musical context. The study is divided into three sections: a description of musical and technical approaches that I have found to function over different P-HDLA installations; reflections on the compromises of lower-order monitoring during the compositional process; and presentation of the “Virtualmonium”: an instrument for the performance of stereo works that benefits from the growing popularity of P-HDLA installations.