for whatever reason I have no idea the exact same commands today work perfectly and I can install Roon Bridge under Volumio again - must have been something messed up in the repositories
This time all that was needed is as follows
sudo apt-get update
sudo apt-get install bzip2
curl -O http://download.roonlabs.com/builds/roonbridge-installer-linuxarmv7hf.sh
chmod +x roonbridge-installer-linuxarmv7hf.sh
sudo ./roonbridge-installer-linuxarmv7hf.sh
I hate computers sometimes 