Hi @rmbn - I recommend checking out the conda env create command, which will allow you to install multiple conda environments. That way, you don't need to worry about overwriting your old environments, and you can always toggle back and forth between environments with conda activate
For instance, you can have the following two conda environments
Songbird / Qurro environments
wget https://data.qiime2.org/distro/core/qiime2-2020.6-py36-linux-conda.yml
conda env create -n qiime2-2020.8 --file qiime2-2020.6-py36-linux-conda.yml
Gneiss envrionment
wget https://data.qiime2.org/distro/core/qiime2-2019.10-py36-linux-conda.yml
conda env create -n qiime2-2019.10 --file qiime2-2019.10-py36-linux-conda.yml
RE Virtual Box, that solution is fine for older Windows versions - but you may want to check out the WSL install instructions if you have a newer computer. From what I have observed, it is much faster than Virtual Box.