Here is how I set up the filters on my 756 PROII, showing Frequency vs. Amplitude plots for both Sharp and Soft, but I prefer the Sharp. Input was white noise from 10 meter band, so not a perfect test. I switch MixW2 to use Filter 1 to look at all the signals in a 2.6Khz slice of the band, then Filter 3 for the QSO using macros that are part of my CQ, Reply, and Bye commands.
Filter 1, SSB Voice Medium, 0-2600 Sharp
Filter 1, SSB Voice Medium, 0-2600 Soft
Filter 2 SSB Voice Narrow, 200-2000 Sharp
Filter 2 SSB Voice Narrow, 200-2000 Soft
Filter 3 SSB PSK31 Very Narrow, 1450-1550 Sharp
Filter 3 SSB PSK31 Very Narrow, 1450-1550 Soft (No difference)