my Father is deaf and is training to be an EMT. however because of his 100+ db loss, there are no amplified stethoscopes he can use and hear with out his hearing-aids in addition so i came up with an idea to use his hearing-aids and a nice set of headphones and it worked! only problem is it took a while to get his hearing aids to stop giving feedback.
i have looked and can't find a open air backed headphone so the headphone doesn't: A damage his $6,000 hearing aids ; B make so much feedback ; C is cost i'm looking at a $200 max budget because the stethoscope it's self is extremely expensive
Maybe the Audio Technica ATH-AD700 Open Air Dynamic Audiophile Headphones : http://www.amazon.com/Technica-ATH-AD700-Open-air-Audiophile-Headphones/dp/B000CMS0XU
they don't make anything (to my knowledge) that could be considered anything near audiophile grade, but you could look into a set of bone conduction "headphones", people with hearing loss say good things as long as his (have no idea how to spell this) choclia is in tact