If the maximun peak to peak input voltage is 40 Vac, then the maximum Ac rms input is 28 vac rms. Over an 8ohm load, this is 100 watts.....good for checking a modern amp at full ouput. However, I need to test alot of older tube amps which need to be adjusted with 16ohm load. At 28 volts, this only allows the amp to be tested at a 50watt load, less than the 75watt load I need. If I use a 10x probe, then pico will see a 5 volt input. In order to see harmonics to calculate a thd of say .01%, then pico would need to resolve harmonics with amplitudes lower than a 1/2millivolt. If I used a high impedance voltage divider across the 16ohm speaker and a 1x probe, I'd need to measure harmonics with amplitudes lower than 2.8millivolts. If the maximun dc input is 20 volts, then pico would need to be able to clearly see a .6millivolt peak for a dynamic range of 90dbv. Can pico do this?