Yes, all these Dolby Headphone amps hiss at certain volume levels. Luckily, adding an extra amp didn't add noticeable hiss, though the Lyr's hum did ramp up overall noise. As long as the amp you use has a quiet noise floor, you won't get extra hiss.
Also certain headphones are great at hiding hiss. The Q701 is one of these. The D7000 is sensitive as hell, so the hiss is noticeable in comparison.