On hearing damage, the Etymotic paper linked above has some good info, such as the discussion of the work of Kujawa and Liberman, indicating that even so-called "temporary" loss may have long-term consequences. However, it discusses only the OSHA standards for work place noise, which should not be applied for home listening. Although it recognizes that the OSHA standard allows for some long-term loss, more stringent standards which all but eliminate this possibility aren't described.

In discussing power requirements I typically emphasize safe hearing levels and am not amused by those who want to be able to "crank it". An article here discussing safer standards has been cited before and emphasizes the inappropriateness of applying a work place standard which allows for some hearing loss to "community" venues such as listening at home. Table 1. there compares the standards, showing the much more stringent ones of the EPA and World Health Organization intended to prevent any significant chance of damage.

Enjoy the music, not the equipment.