Not that we'd need all the knobs...
But there was a time when engineers were striving day and night to allow the optional tweaking of sound while remaining into acceptable specs : it was far more of a battle than the yearly ICs swapping which the consumer audio market has shrinked to since the mid 90s.
As the patchbay suggests (and the literature) this was meant as professional gear, or more practically : "pro-sumer".
The included Head Amp was a novelty, as in the contemporary CA-1000 from Yamaha, and its presence even confused High Fidelity Magazine who thought it was... tape-related.
The circuit consists of a two-stage DC differential flat amp, two-stage NFB + CR EQ section ; the attenuator has ±0,5dB L/R accuracy.
Beyond the many filters, turnovers, bells, whistles, front inputs and related pot, the TAE-8450 hides on the other side input level trim pots for all line inputs (individually) and a 4-step phono input impedance trim.
The meters... ah, the meters : Sony's PPM, Peak Program Meters, are the best and most readable ever made. Here with the addition of sens(itivity) and brightness adjustment pots.
A tradition at Sony since the very late 1960s, a measurment inspection card was delivered alongwith the unit ; all the cards I could see exceeded the published specifications :)
This incarnation of the ES-II design, too, was ahead of its contemporaries - probably a little too much for many a potential buyer.
But at 285,000¥ the TAE-8450 obviously couldn't become a best-seller and it vanished along the other V-FET / PPM series all too quickly.
The complete description of the features, the specs and a 1975 USA review you can find on Samuel's hi-fi page.
You will also find three little video clips showing the PPM meters in action !