I do extensive audio editing on my Macs
You should learn to edit and clean your audio rather than just convert it.
The two programs I tend to use most are Soundstudio and Amadeus Pro
I have used both for years, unfortunately neither has everything that I want and I usually use caf files as intermediaries between the programs and then convert the file at the end.
Either will allow you to edit, denoise (not as well as professional APPs), and view your audio. try playing with demos if you can find them. Soundstudio's old demos could save but Amadeus's did not.
I have more experience with sdss, but it has some limitations. I do prever its Noise Gate, Dynamic Compression and Equalization filters and have used Reverse many times when digitizing cassettes. You need to add LAME to write MP3's, nt a big deal.
Amadeus Pro has some filters that work well and can rip from and to MP4 files, but its interface is harder for me for routine cutting and pasting - so i use both programs.
They both allow you to add in outside filters, but these are usually either expensive or not well kept up.
Sound Studio 4 for Mac - Felt Tip
HairerSoft - Amadeus Pro