MD1 VA0-2 have its internal amplifier clipping from too much gain, this has nothing to do with the OSSC.
If I had to assume, the OSSC has no load in any form before its ADC, so for the unusual MD1 VA0-VA6 “speaker”-output one would have to add a load… any load, which can be added to the scart plug itself.
1k on each line would be good.
Model1 Scart Plug
Just solder 1k resistor between pin 2 & 4, and pin 6 & 4.
Note that Pin 2 and 6 wired to the tip and ring of the 3.5mm plug, pin 4 is ground.