Title says it all, probably a newby question, but I have noticed there are different Ohm versions of headphones and such and I was wondering...   What are the differences of these headphones and what do higher/lower Ohms do for listening experience?

Firstly, hello esteemed population of Head-Fi, I am deadofmind ^_­^   I have in my possession a pair of Sennheiser HD 280 Pro 64 Ohm headphones. When I purchased them I used them solely for music and communication-less gaming.   Now however, I would like to Mod my headphones to have a...