No disrespect intended, but that is absolutely user error. OT does not magically have a preference or dislike of “certain synths”. If your waveform in the AED looks like a block, it’s because you recorded too hot. If your waveform is not a block, and the output is distorted, check the gain staging of the OT, your mixer, interface, etc. Turn it down! I sample an arguably super-fat OB-6 all the time, and it sounds great.
This thread has been fun, but also makes me want to pull my face off. To be sure, the OT converters impart some (relatively neutral) coloration, but what machine doesn’t have its own sound? Is this real life? It’s the weird unsubstantiated claims like this that keep the myth of “OT sounds bad” alive on the web. Just learn to gain stage correctly, and enjoy the OT for what it is. Your samples shouldn’t be distorting. OT fidelity is fine. If you need something better, save up for a Kyma system.
Just my 2c. Carry on!