I've got these fitted into my kitchen cabinets, and I've got to say they are a compromise. If you can possibly use freestanding speakers I'd say you should.
As for positioning, have you tried moving your rears around? WHF advice would suggest (if I recall rightly) NOT having them high up. Certainly when I experimented with this I ended up with the rears on the floor (in itself not a great idea) rather than high up.