So I thought it would be good if I will buy Beyerdynamic DT 770 and order C5D Amplifier + DAC, would be better then beats pro?
+ it would 60$ cheaper,
any thoughts or suggestions?
I don't think the beyer dt 770 would be a good choice for on-the-go as I am pretty sure the 3m cable is non-detachable (not 100% sure though). The HE-500, mad dog/alpha dog, and AKG K550 are all unsuitable for portable usage. You should only stretch to your full $600 budget if you are looking for a very nice audiophile neutral-sound-signature pair of headphones for home-use that requires an amp/dac to sound good (eg. HE-400/alpha dogs/Q701/HD600/HD650 or better)
For on-the-go, you want portable, closed options. You can acquire "best-in-the-mid-fi-class" portable, closed headphones at $200-300. Throwing any more money than that at your closed/portable will not give you much improvement in sound quality. Some popular options worth investigating include: Sennheiser Momentum Over-Ear ($300 on sale), nad viso HP 50 ($300), kef m500 ($300), akg k545 ($200 on sale), and the sony mdr-1r ($200-or-less). If you are a basshead, you can consider the V-moda M100 ($300ish) + $20 XL pads. Any of those options without a dac/amp will significantly outperform the beats pro. note: the akg k545 performs just as well (if not better - according to some people) as the $300 offerings if you are looking to save money.
Personally, I don't think it's a good idea to invest more than 50% of your budget into a dac/amp, but that is a personal opinion. I personally think you can even skip the dac/amp at this stage too for if you want to save money. The portable/closed mid-fi headhones on the market these days are designed to be able to be sufficiently driven out of your mp3 player/smartphone/laptop 3.5 headphone jack, so you do not really need an amp. The improvement in sound from an amp/dac is marginal compared to your upgrading your headphones, but since your budget does stretch that far, I guess you can go for it. [tho if I was in your shoes with that budget I would skip out on the portability & spend the money on a nice set of open headphones for home use ($220-400ish) + amp/dac($100-200ish)+cheap closed/portable($100-200)]
If you do decide to get an amp/dac, I personally think you should stick to an entry-level budget portable amp/dac for mid-fi, closed headphones (definitely sub-$200, around the $100 mark)... unless you are planning to upgrade to a nicer more-high-end set of home-use headphones in the future (such as the alpha dogs, q701, he400/he500, sennheiser hd600/650 etc). Otherwise, I think getting the JDS C5D is kind of a waste of money [personal opinion again lol]. Remember you need higher-end headphones to hear a significantly noticeable sonic upgrade to make your dac/amp investment worth it. Most higher-end headphones are geared for home-use, so you can get a more powerful desktop dac/amp rather than overspending to get portability. Mid-fi headphones generally will not scale up that significantly as they are limited by their drivers & closed design, so there is no reason to throw a lot of money at your dac/amp.
My recommendations for portable amp/dac set-ups if you are still interested would be Fiio E17 ($130) vs the E07k ($90) vs. Audioquest Dragonfly 1.2 ($150). However, you can get older modes for significantly cheaper such as the Fiio E7 ($70) vs E10 ($75) or Dragonfly 1.0 ($99).
edit: I am unsure of those DACs compatibility with the iphone as I do not have one, it would depend on your iphone version as well. From a quick search, I believe that the iphones w/ the new lightening connection would not really be compatible with most DACs, so you can either spend even more money for something that is compatible or just skip the dac. If you are only using your dac/amp with your iphone, you need to do some more research on what dacs are compatible w/ your iphone model. Personally, I would just to skip the amp/dac. From my experience, I have not noticed a significant sonic upgrade for most closed mid-fi headphones that was worth an extra $100+.
Sorry for the long wall of text, but I hope the information was helpful. Please let me know if you have further questions or want impressions on stuff I've owned.
