I cannot find 26dB gain in the sensitivity menu. Is it available in I-Tech?

Yes, many different sensitivities and gains are available depending on the setting of the max input level switch. Refer to the I-Tech Application Guide for a complete list of all 149 sensitivity / gain settings. 

To set the I-Tech amp for 26dB gain, change the max input level switch to 20dBu using IQwic or the front panel display. Upon returning to the sensitivity menu you can set the gain to 26dB.