We report the results of piezospectroscopic studies of bound multiexciton complexes in silicon doped with phosphorus, lithium, and boron; and of biexcitons in pure silicon. The bound exciton and bound multiexciton complex spectra are interpreted with the aid of a simple extension of the shell model to the case of non-zero stress. Many new results were obtained and almost all have been explained by our model. The lithium spectra are very different from those of phosphorus, as expected in the shell model since the valley-orbit states of the two donors are ordered differently. Large differences between the relative intensities of the lines in the boron phonon-assisted and no-phonon spectra are explained by a new treatment of the no-phonon process for boron complexes which relies on the fact that in an indirect gap semiconductor no-phonon recombination must proceed via the k-space tail of the electron or hole wavefunction.