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Question: Advice on AH-D2000

I purchased the Denon AH-D2000 today and haven't heard them yet because they are in transit to my home. I have read and researched extensively about these phones and the only question I have left is, will I need an amp? Currently I have a beefy 1200 watt 7.1 home theatre system made by Onkyo and am hoping/wondering if the (phone) input jack will be sufficiant enough to power and release the AH-D2000 to their peak performance? If not, what amp will enable the phones to perform as close to flawless without breaking the bank?