Hi Imir,
To print a book cover with at least 70cm printing area all of those SRA3 toner devices are too small, even if someone may say so.
The best quality and biggest size (something which you need to print an attractive book cover) you get with a Fujifilm Jet Press 720, in the North American market this device is called JPress 720. It has a paper size of up to 750 x 530cm and the max imaging width is 733, in photo-quality. The productivity of that digital inkjet press is attractive for runs from 1 till 3000 B2-sheets
Fujifilm has installed those digital presses in Japan, North America and Europe, and I can help you getting in contact with Jet Press user if you like.
Cheers
Wieland