Symetrix have a very large Tech library that includes both current and discontinued stuff
http://www.symetrixaudio.com/index.php?Show=11
and
http://www.symetrixaudio.com/repository/
I happen to like it when manuafacturers give good flow charts for the equipment so you have good knowledge of the internal workings
http://www.symetrixaudio.com/repository/302-flow.pdf
this one may only be a simple 2017 unit but at least you know where everything is and how it intererelates ... even the nature of the output