I assume you are refering to a tool for voice isolation and instrument removal?  AI audio-enhancers would be the best way to go about processing the singing voices to increase their quality, short of having someone sing them or an expert rework the audio.  However, there are many limitations to enhancing music using any post-processing methods.  Thus, I would suggest using higher quality vocal extraction tools or ideally have someone sing the acapella for you.

You can find a vocal extraction tool that is considered to be high-quality based on internet reviews and highly rated on TrustPilot at: https://www.lalal.ai/
You can find singing services at the following website: https://www.fiverr.com/categories/music-audio/singers-vocalists

I hope you found that helpful.  Is there anything else I can do for you?
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