Fellow 'noob' here - quite a bit older (44) - but enjoying my mid-fi. I'll be picking up my new 840's in a couple of weeks - so can give you some comparisons then. I do use an E7 - and so far with the cheaper Senns I have - it has helped clarity and separation. Could be placebo - haven't DBT - but I'm happy with them, and that's all that matters. The E7 has definitely helped with my home PC and netbook.
Couldn't help noticing that you mentioned that you have 2 sources - ipod and computer (if I am reading it correctly). Also that you mentioned you've been having the problems on most of your headphones - and it always happened on the computer. So I'd suggest maybe look at the source first (and isolate the steps in the chain).
Suggestion - can you take your 840's to a friend's / music store / or someone you know who has a 1/2 way decent CD player and amp. Take some music (pref CD) that you know - and play it. If you're still getting the issues - then perhaps it was the cans. I'd be willing to bet that the issues will be gone though. You then need to look at your source. If you can borrow a DAC from someone in your area - plug that into the lappie - and see if that helps. If it does, look at buying the E7 - cheap, good entry DAC chip, and can be used as portable amp and DAC.
Second - I have permanent tinnitus. Most of the time I don't notice it - and it hasn't stopped my enjoyment of music. If you are really listening to your music very loud, consider turning it down a bit if you can. That way you'll still be enjoying your music well into later life as well. I just wish someone had given me the same advice 25 years ago
thanks for that advice. the unfortunate thing is i we don't have any serious music stores in my home town i can go check out. and i don't know anyone other than me who likes high end audio. everyone has beats and doesn't even know what an amp is. but a CD player may be possible.