That Sabre ESS9007 DAC is highly efficient in quality compared to burr brown dac in v685.
When I auditioned them, I certainly could feel the difference. But then I felt a difference between 3080 and 1080 too. Sabre pro 9026 is a class apart.
In your case, need to figure out what challenge you have. V685 isa very capable amp and it should not have any challenge driving S20s. Dont trust YPAO much, it's calibration is average at best. Are you struggling in stereo mode or 5.1 mode as well? Try settings in AVR - some combination here and there might work, what are other equipment in your setup?