Years ago I owned a QSD-1, but sold it, partly because I needed the money, partly because I didn't have a lot of QS LPs, and partly because I was sick and tired of the loose circuit boards.
I just won a (supposedly) mint QSD-1 on eBay. Looking for a service manual (which I gave away with the unit), I found this group.
I am an Ambisonics person, lock, stock, and barrel. But I enjoy surround recordings in other formats. Having owned both the Space & Image Composer and the Tate-Fosgate unit, I have to say that I much prefer SQ to QS.
The reason is that SQ never needs lateral enhancement -- only front/back. And the ear isn't anywhere nearly as sensitive to anomalies in front/back directionality. Even with the multi-band QSD-1, you can plainly hear lateral image wander. It's annoying.
I have a 100V QSD-1000, which I "modified" to 117V by sticking a power resistor in series with the transformer. I've never been able to compare it with the QSD-1, but my gut feeling is that the QSD-1000 is cleaner and more transparent. If I can find a manual, I might modify the QSD-1 to replace the electrolytic coupling caps with Mylars or better.
I live in Renton and have a Really Good system.