WTF?? I only presumed you understood that quoting those measurements shows that Pre90 can deliver output that high with very low distortion, not that it would have to deliver same to offset DIRAC gain losses.
But you will see here that KR did experience gain loss ".....of almost 20db!"
I may be wrong but it looks to me that no matter how this charted data is interpreted
https://www.sowter.co.uk/decibels.php , an "almost 20db!" gain loss would conservatively require at least ~ 6.2 v-or 2.1 v more than KR's Exasound s88 DAC's balanced outputs could deliver. And, again, I could be wrong but it also appears that his power amps' input sensitivity was not sufficient to offset DIRAC's imposed gain loss. Thus, the need to place a preamp with sufficient output between the DAC and the power amps.