A company call HeadRoom sells a headphone amp. It may be over kill for what you need, but it might be worth checking out. The amp is called the Total Air Head and can be found at www.headphone com.
why do you guys need this? a GOOD set of headphones will eliminate the need. I found out the hard way. 1 boosteroo and 1 radioshack version do not get use anymore, except when I am showing something on a portable dvd player and need more jacks.