To selectively back up iPhone music to external Hard Drive/iCloud/DAS/NAS using DearMob iPhone Manager, all you need to do is change the default backup location before you select iPhone songs for export and backup.
Step 2: Connect your iPhone X/8/7 to computer via lightning cable;
This iPhone backup software will auto-detect your iPhone iOS device and build connection. The available storage, iOS version and battery status will also be presented for your consideration.
Step 3: Click gear wheel icon on the top right side;
A dialog window will pop up providing settings on Path and Options
Step 4: Click the "Pen" icon to edit default path for each items.
You can set the default export path of iPhone photo, music, video, and other data to target external hard drives respectively.
Step 5: Click "OK" to apply changes.