Did you mean you are getting only 75 dB peak with volume at -20? Did YPAO set the L/R speakers to level 0 or did it bump them up?
Assuming you are getting 75 dB average, not peak, with volume at -20 then I would say the ATI amp would not result in audible improvements. If you want to listen at or above 85 dB average with peaks to 105 to 110 dB (probably at the limit of your speakers), then I believe there will be audible improvement, mainly because the Ascends are 4 ohm nominal speakers. They don't dip below 4 ohm, and the phase angles look benign, but they can benefit from a 200 W 8ohm, 300 W 4 ohm ATI amp for sure. You would likely gain about 2-3 dB headroom practically speaking, in 2 channel applications, more for multi channel.