This paper presents a study of classification and EEG feature improvement for a spatial auditory brain-computer interface (saBCI). This study provides a comprehensive test of a head-related impulse response (HRIR) cues for the saBCI speller paradigm. We present a comparison with previously developed HRIR-based spatial auditory modalities. We propose and optimize the three types of sound spatialization settings using a variable elevation in order to evaluate the HRIR efficacy for the saBCI. Three experienced and seven naive BCI users participate in the three experimental setups based on ten presented Japanese syllables. The obtained EEG auditory evoked potentials (AEPs) result with encouragingly good and stable P300 responses in online saBCI experiments. We analyze the differences and dispersions of saBCI command accuracies, as well as the individual user accuracies for various spatial sound locations. Our case study indicates that the participating users could perceive elevation in the saBCI experiments using the HRIR measured from a general head model.