I'm pretty sure those are high/low impedance switches in an odd place. According to the SE34I.3 manual, it doesn't have impedance switches by default. It looks like you have configuration 5: dual volume with four inputs, plus an additional set of impedance switches. There's a chance that these have UFO transformers added which I believe are when impedance switches became a standard thing.
https://www.decware.com/newsite/SE34I3owner.pdfEDIT: never mind, saw the comments in the other thread.