My understanding is that the few internet based authorized dealers are subject to the same constraints as the stores, which is to sell at the list price. The reason some of the internet sites sell for much lower is because they are unauthorized and that is the only to get any business.
I believe you can generally get warrantee work done with unauthorized purchases but you have to go directly through the vendor who sold the equipment, not Denon.
In the end its typically price versus the comfort level of having Denon service the warrantee. If you could easily get both, no one would pay list or buy unauthorized.
However, if you are good at haggling and you have multiple local stores that sell Denon, you might be able to get 10-15% off list from an authorized dealer. A happy medium if you can pull it off or have any contacts within any of the stores.
