For sound normalizing you can use normalizer in Cinegy Air.
To send audio from sequence to external software and back to sequence after correcting it, you can export only audio track to WAV from the sequence, edit, re-ingest and add it to the sequence as an additional audio track. Then delete the original sound.

For the third party solutions please refer to: http://www.minnetonkaaudioshop.com/ or https://www.magix.com/ca/music/sound-forge/