Yup, Superwound was launched as another brand name of strings from the Rotosound factory. They had the same address back then.
Rotosound still makes piano-string design strings as the PSD sets. They are the same as the old 606 Superwound sets (stainless round wound). 707s were flatwounds, must have been pretty rare. I loved the 505s which were the best pressurewound strings out there.
I think Superwounds sound fantastic, but it's challenging to get the right fit, as the length of the string past the bridge pieces is really variable. You also need to do some special setup on the bridge height to make up for the exposed core end.
David Fung