We just made measurements with sp200 as well. It's prone to the issue because the low gain option is 6db. There is no 0db or -10db option. ...... high gain is whopping 18db.....
Great sounding amp, though.
If someone could come up with a detailed resistor swap, that would be heavenly. That is beyond my abilities, esp without a circuit diagram.
I've tried talking to the USA seller, but of course no response at all.