I recently paired my Sennheiser HD6XX cans with the FiiO Q5 DAC/AMP. The Q5 is a fantastic piece of equipment but perhaps a bit on the pricey side for most. Would love to see this as a drop.
I know it probably is not an option but my suggestion is to try to create a relationship with McIntosh Labs. They have a strong preference for dealer installation of their products but there are a few things that can be purchased on line. I would suggest something with great utility to begin a relationship with them like a receiver.
Why ask people? People don't know anything. They don't know what they want until you give it to them. Were Sennheiser and Audio-Technica not the expected results?..
It's unfortunate because neither of those companies make anywhere near the best sounding headphones at any price point. Just the most marketed and further popularized - now forget just being marketed on here...
http://item2.gmarket.co.kr/English/detailview/Item.aspx?goodscode=932554623
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https://www.sonicelectronix.com/item_89648_FiiO-E10K.html
If you call up Sonic Electronix, I'm sure you can easily enough ask for a price reduction of at least $5.
The first site is one of the biggest online distributors in South Korea - perfectly safe. I think they're actually owned by eBay. The only catch with these headphones is that the brackets which hold the cups eventually dry up and snap, which will cost you an additional $35 (using a first time purchase coupon) to order 3D-printed replacements which you can easily enough then attach). You can find them here: https://www.shapeways.com/model/upload-and-buy/3381309?mg=6&c=2&f=1
They're otherwise infinitely comfortable (probably the only pair of headphones I can wear forever, as far as pressure or sweating would be concerned), even if a bit finicky as far as feeling confident about their placement on your head.
Total ends up being ~$153 for the headphones + a DAC/headphone amp with digital passthrough, line-out, and bass boost. If you ever come across a pair of headphones for $250 or less which you can plug in directly to any generic sound interface you may have in your devices, please let me know and I will eat all my Sennheiser headphones.
PS- For this setup, use the bass boost on the amp.