That's a great question. I can't say for sure. I own NHT 1.5s, and I know what you're talking about. My Pioneer VSX-1015 powered two pairs of those and an NHT center channel just fine at my normal listening levels, but it sounded strained when I played it louder than normal. I got a separate amp for the front two channels, and that made a noticeable difference at louder levels (but not at my normal everyday listening levels).
You have a better chance of them being okay during stereo playback than during surround sound because you'll only be powering two speakers (so it's less demanding on the receiver), but I can't say that it'll be sufficient for you. The 665 is rated at 90W, which is less than my Pioneer was - but those ratings don't seem to be consistent from one manufacturer to the next.
The 665 (and higher models) has pre-amp outputs that would allow you to add an external amp if you decided later on that the receiver wasn't sufficient for you. The lower models don't have those.
My biggest suggestion is, if there's any doubt, buy the receiver from someplace that will let you return it and won't charge you a restocking fee. That way, you can try it out at home and see for yourself without financial risk.