In the UK, where I'm from, in law your contract is with the dealer. You're not buying it directly from Denon, so it doesn't matter if they say 'only buy it from our approved dealers'. As long as you get in writing how long the warranty is, and how much cover is provided with the warranty - from the dealer you're buying it from - they are legally obliged fulfill that warranty, regardless of what Denon says. Buying the product with a credit card offers you more protection.
As I said earlier, this is how it is in the UK, and it might be different in the US.