The rubber bumpers are included with your 5DB and you manually attach them to the speaker itself (they have a sticky back). 

I think you may need to mock up a floor plan for us.  Not sure I fully picture "same plane as the front speakers"?

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Speakers: Aperion 6T, 6C, 5DB, 6IC, Bravus 10Dx2
Monitor: JVC RS20U front projector with Stewart Velux 100" screen
Receiver: Yamaha RX-V1800
Blu-ray: Yamaha BD-S2900
Amplifier: Emotiva UPA-7
Conditioner: Panamax M5300PM