If you're looking for a platform to use AI to help composers expand on their original music tracks, ExtendMusic is a good option. It uses generative AI technology to expand and augment original music compositions, generating new ideas and sounds based on music files users upload. The service is free to try and takes about a minute to get started, so it's a good starting point for musicians.
Another helpful option is Cryo Mix, an AI-based music mixing and mastering service. It's got tools to improve audio, including AI Mixing to boost vocals, add backing vocals and otherwise tweak settings, and an AI Audio Separator to split a single audio file into individual stems. The idea is to make high-quality audio production possible even if you don't know the first thing about audio engineering.
If you want to make music with different voices, Musicfy is worth a look. It lets you create high-quality music with AI voice artists and tools like AI text-to-music conversion and stem splitters to split tracks. Musicfy also offers royalty-free music albums and a variety of subscription plans depending on your needs.