Ideally, you want a headphone output with the lowest output impedance possible and definitely lower than the nominal impedance of your headphones. Otherwise the frequency response will be modified by the impedance curve of your headphones (among other issues). Here's a post from Headphonesty with some good information - link.
However, that's not to say that the DT770's won't work well with your receiver's headphone jack. If you're not satisfied with the sound you're getting, you'll probably have to consider adding a dedicated headphone amp to your setup.