IDM is using a ftp connection as well to download the data. Your slow download speed is not coming from using the ftp protocoll, but not using multiple connections (segmented download). This is what IDM is doing by itself. It splits the file you are downloading and downloads multiple parts at the same time. Hence the increased download speed. Instead of awkwardly copying the download link, you should set up smartftp to do exactly this, segmented downloading. It's a bit late, so I make it short:
1) start your download in smartftp
2) in the transfer queue window (bottom) set the workers to 10
3) right-click your download in the transfer queue window and choose properties
4) go to advanced
5) set Multi Part Transfers to enable
You might have to experiment with the settings of workers in the transfer queue window and the number of workers/part in the properties window. If you want to know more i can make some screenshots tomorrow.