[NotaLefty]

Hi, I just dug up an old Pioneer VSX-451 to try and power some Sennheiser HD700's. The receiver is connected to my computer. When my headphones are plugged in, I get a loud hum and white noise. Hopefully this is a simple fix... anyone have an idea as to what's wrong?
 
Also, would using this receiver provide any benefit over having it directly plugged into an Asus Z87-C motherboard?

 

[Sil3nce]

Drop the receiver, unless you're planning to power a pair of near-field bookshelves. I'm not familiar with that particular model, but based on specs, I wouldn't put my HD700s anywhere near it.
Spend the money, buy a nice dac/amp. Or something relatively cheap, that actually pairs well with the HD700s. Like the HRT Microstreamer. 
Don't spend 500+ on a headphone, then run them straight out of your mobo. Not worth.

 

[kramer5150]

You could try plugging into the ASUS integral sound card... Hopefully that will at least alleviate the hiss and noise.
 
I doubt it will do those cans justice though.  You're going to need a better DAC and amp to push the HD700 correctly.