Why does USB have so much less audio output than LSB? I've checked all settings and they are correctly set or not used, like AGC etc. Using same band pass on both modes.
Not knowing your level of experience with the various amateur radio modes, be aware that for a given SSB (single side band) signal, only one of the side bands (upper or lower) is transmitted. The carrier and the other side band are significantly suppressed in the transmitted signal.
Since USB (upper side band) tends to be used on the higher frequency bands, you may simply be experiencing the difference in gain of your DSP or your antenna system on these higher frequencies. Normally, a properly configured AGC block will minimize this variation but it cannot completely eliminate it.