Part of the famous Series 20, available well into the 1980s, the D-23 was advertised a lot, sold ok but not that much in the end. It was preceded by the SF-70, later complemented by smaller equivalents like the D-70.
Hifi Exclusiv made a big test for its may 1979 issue : the other units tested were the Sony TA-D88B, Accuphase F-5 and Mark Levinson LNC-2. The winner of this test was, sorry guys, the Sony.
The test however shows a better s/n ratio than spec'ed by up to 5dB, some divergence on frequencies depending on volume/slope (mainly at 500Hz which in fact turns out to be 466Hz, so a 6,8% error) and some overshoot at the 18dB slope due to the Butterworth structure.
The specs here published are a mix of of those from Pioneer and those from said test - a bit more accurate ;)
The dedicated japanese catalog is now at hand (2011) but nowhere near being translated...