Calculates the American National Standards Institute (ANSI) S3.5-1997 Speech Intelligibility Index (SII) (ANSI 1997, (ANSI, 1997)), a standard method for computing the intelligibility of speech from acoustical measurements of speech, noise, and hearing thresholds. This package includes data frames corresponding to Tables 1 - 4 in the ANSI standard as well as functions utilizing these tables and user-provided hearing threshold and noise level measurements to compute the SII score. The methods implemented here extend the standard computations to allow calculation of SII when the measured frequencies do not match those required by the standard by applying interpolation. Furthermore, the package now includes a native, highly optimized C++ implementation of the canonical Moore & Glasberg (2004) specific loudness model for impaired hearing, which structurally mirrors the bramslow2004 implementation from the Auditory Modeling Toolbox (AMT) to calculate loudness in perceptual sones. It also includes advanced methods to predict aided SII based on hearing aid prescriptive rationales, introducing Open-NL (Open Non-Linear), a novel theoretical optimization framework. Open-NL utilizes a Nelder-Mead simplex algorithm to maximize the ANSI SII metric, subject to computational physiological loudness penalties and simulated hardware Maximum Power Output (MPO) constraints, to derive theoretical gain targets. The package also provides functions to calculate real-ear insertion gains, estimate maximum power output (SSPL90), and prescribe dynamic range compression. NOTE: This package is explicitly flagged as a non-clinical academic tool designed exclusively for theoretical modeling and simulation. It has not undergone clinical validation and is strictly contraindicated for general clinical fitting. Unapproved use for direct patient care is prohibited. Any application of this tool to human subjects must occur exclusively within the strictly controlled context of Institutional Review Board (IRB) approved research studies. Development of this package was originally funded by the Center for Bioscience Education and Technology (CBET) of the Rochester Institute of Technology (RIT).