Fusion Drive: Restore from Time Machine - "The disk can't be erased."

Hello,

On a new (late 2015) iMac I need to erase my 3TB Fusion drive (El Capitan, not encrypted, just 1 partition, no Boot Camp partition), and then restore a Time Machine backup (made on a previous iMac, also with 3TB Fusion drive (El Capitan, not encrypted, just 1 partition, no Boot Camp partition).

According to Apple document: https://support.apple.com/en-us/HT204904 "Restore from a Time Machine backup" I...

1. restarted with cmd+R (later I also tried cmd+alt+R, and also from a bootable El Cap USB flash drive)

2. selected "Restore from Time Machine Backup"

3. selected my external Time Machine backup drive

4. selected the most recent backup

5. selected "Macintosh HD" as destination and clicked "Continue"

... but then the following message appeared "The disk can't be erased."

Then I tried to erase "Macintosh HD" via Disk Utility:

1. restarted with cmd+R (later I also tried cmd+alt+R, and also from a bootable El Cap USB flash drive)

2. selected Disk Utility

3. selected "Macintosh HD"

4. clicked "Erase" tab

5. clicked "Erase" button

... then I got the error message:

"Erase process has failed... Details: Unmounting disk3 - Removing Logical Volume from Logical Volume Group - Unable to delete the Core Storage logical volume. Operation failed..."

I was in the "Recovery loop", and the only way out was to "Reinstall OS X", but then after many hours, there was again my old flubbed installation with everything I wanted to get rid of!

How can I restore my Time Machine backup - nothing more or less - to my new iMac?

I've lost 3 days now with this problem. I really hope someone has a solution.

Many thanks!