Recently I've been taking a look at both the Gilmore Lite and several Creek amps (OBH-11 in particular). What I want to find out is if there really is any need for or benefit with dual headphone outputs. I suppose it's helpful if listening with a friend, but will it decrease quality or volume if two pairs of headphones are plugged in, and -- as I mentioned before -- are there any benefits beyond this?
It'll help when you want to A-B a couple headphones.
Plugging a second set into the amp may or may not affect the first; it depends on the amp. The Bithead can power two headphones at once, so it can't be too difficult a feature.
Be careful when using two different headphones. Their impedence values may be different, which will make their volumes different. You don't want to blow the more easily driven can while you listen to the more power hungry one.