First of all, thank you for using our software. Secondly, we are sincerely sorry for the issues you mentioned.
Sure. you can de-drm with KCR Converter and then convert them with Ultimate. But the quality will be the same.
If you have used Epubor Ultimate to remove drm from kindle books successfully before, you can try this way: https://www.epubor.com/remove-kindle-drm-on-macos-1015-catalina.html#part1
