Honestly, I think Sansui got most of it right across their lines. At least to my ear.
I’m not an expert but I’ve listened to and/or owned some of the following Sansui models:
Receivers: 7070, 9090 & G7700
Integrateds: AU-517, AU-717, AU-719 & AU-X1
I enjoyed them all within their intended use and limits.
I’ve also had many modern well regarded integrateds in here - Yamaha A-S801, Yamaha A-S1100, Marantz Reference PM 14S1 & Peachtree Audio Nova 150 to name a few in the lower price range.
As much as I liked all of them, the AU-X1 slayed them all.
I currently own the AU-X1 and have the Yamaha A-S801 in my second system. This Yamaha has spectacular AP bench test measurements but it cannot touch the X1 in organic, realistic SQ. I’ve never seen AU-X1 measurements on an Audio Precision but I would love to. Maybe then I could determine where the magic lies, but I’m guessing that even then I won’t. Just like speaker measurements, there’s more than meets the eye.
It’s hard to describe how good the X1 is. I’ve heard a lot of different amps driving my 805D2 (here and in showrooms, some of those units were well above the level of the gear I mentioned previously) and I’d put the AU-X1 up against anything. I wish I knew what spec to look at so that I could identify my next amp purchase.
Not bad for an integrated from what some call a “mid-fi” manufacturer in 1980... Even inflation adjusted it’s taking no prisoners.