Hi tf11972
As I understand it, Tutti in organese means pulling out ALL the stops AND couplers. It you then play some chords with both hands and feet then you are putting the maximum possible stress on your audio system. It is possible that it does not like it and you may get clipping - it is also possible that your amplifier's power supply cannot fully cope with maximum power for more than a few seconds - further promoting clipping and loss of volume.
Very few amplifiers or speakers are rated for continuous maximum power and damage could also result.
Further it is likely that your hearing (which has a logarithmic response to volume) gets used to the loud noise and you are no longer able to tell what volume you are hearing.
Another less likely possibility is you are putting a high load on your computer's cpu and it could be overheating.
csw900