How are you generating 26,000 Hz tones?
NCH Tone Generator only does 44,100 samples per second at 16bits if you are doing CD-Quality stuff, up to 192,000 samples per second but still at only 16 bits, which doesn't make sense when 96 kHz and 192 kHz sample rates are generally found in Nature at 24-bit sample bit depth.
Anyways, what are you generating 26,000 Hz tones with what bit rate and sample bit depth etc. and what equipment do you have getting the tones in the PC sound card out to the patient?
The kind of tinnitus I have is all like crackling bones not so much frequency loss, how can your set-up help me? In headphones it sounds one way but in dead air a totally different way. weird that