Freelance Author needs a cover for a tech book

Freelance Author

is looking for a cover for a tech book

I am looking for a book cover design that I can use for an ebook series. The first ebook is already on the market, I'm attaching the old cover. It somehow "grew" into this state (which I want to change). The target of the competition is to find a design which just needs to swap the different devices I'm explaining in the ebook. The first one would have to show the four current Kindle models. You can find pictures of them on the Amazon press site (http://phx.corporate-ir.net/phoenix) resp. at Kobo.com. The second one should show pictures of the Kindle Fire HD (7 / 8,9 inch), the Amazon tablet. The third one is about the Kobo eReaders (Kobo Touch, Kobo Mini, Kobo Glo) The titles are:
"Kindle" resp. "Kindle Fire HD" resp. "Kobo"
Subtitle
"Das inoffizielle Handbuch. Anleitung, Tipps, Tricks"
Both should be as similar as necessary to make clear it's the same style, same author, same quality - and still be distinguishable.
You could work with the official photos of the devices or with illustrations. I'd be happy to see all your ideas. It should look modern. Also, keep in mind that it must be readable in small form in an Amazon listing / preview.