If you're looking for an ExtendMusic alternative, Musicfy is worth a look. It's got a lot of the same AI abilities -- custom voice generation, text-to-music conversion, stem splitters to isolate tracks -- and also offers royalty-free music albums for creative projects. Its interface is designed to make music creation as easy as possible.
Another good alternative is Kits, a collection of AI audio tools that's designed to help you make music more easily and creatively. It's got tools for cloning voices, generating AI singing voices, removing vocals and a library of instruments. That means you can make music without spending hours in the studio.
If you want to try AI mixing and mastering, Cryo Mix has a lot of tools to improve audio. It's got an AI Mixing tool to create a finished mix, an AI Audio Separator to isolate stems, and a mastering tool to fine-tune your sound. It's designed to let people of all skill levels create high-quality audio.