Dale: There are so many types of amplifiers (and DAC’s with amplifiers) that there is no shortcut for studying all of the options, unless you settle for the most generic approach. Important things to consider are power – if you don’t have enough power for your headphone and the dynamics in the music, clipping will result. Sometimes the clipping is “soft” and not readily noticed, but eventually you would discover that much of the detail goes missing or gets veiled with limited dynamics. Another consideration is whether to use a DAC, which may be a separate DAC or built into the same enclosure as the amp. Most DACs will improve the sound over the DACs that are built into computers, but when a DAC is available to replace the DAC built into most cellphones and low to mid-priced music players, you can usually expect a much greater improvement.

Mid-range: Many headphones that cost between $50 and $130 include improved sound and useful smartphone integration (like custom EQ controls). In this price range, you’ll also see a big jump in the quality of materials used, which improves both the sound and the luxury of each pair. If you need a pair of well-made headphones with basic noise cancellation, you’ll need to spend at least this much.
Portability can mean many things, such as appearance in public, having a secure fit so the headphone doesn’t shift off of your ears, amount of isolation from ambient noise (including active noise canceling), whether the headphone can be worn around the neck when not listening or it requires a carry case, and when extra amplification is required, whether a suitable amp can be found that’s OK to carry along with the portable music player.
Be sure to assess the build quality of your prospective headphones. Some earbuds and portable devices are relatively fragile, for instance. If the headphones fold up for easy storage, are the hinges robust, or will they fall apart in a month or two? Don't forget to consider that the earpads and earbuds will get extensive wear and tear over the life of the headphones.
I’m a former Mixer and DJ and I’d highly recommend the Beyer T1 for mixing. It is not absolutely flat, but it is an all around proper Audio Technicians Headphone. For flat response, I might eyeball the HD800 but the low end might not be the best if you are often mixing tracks with solid low ends. Flat might not always be the best option ( my opinion ). If you need to mix heavy bass tracks, it is better to have a headphone that responds better to low end EQ and is generally accepted as a more well rounded headphone.

Despite big promises from Bluetooth’s only Hi-res codec, the standard doesn’t really deliver at best, and it falls far short with its basic 330kbps setting. Both the 660kbps and 990kbps connections offer decent quality, but the 330kbps setting has a lot of noise—and a comparatively poor frequency response with higher-def content. You probably won’t hear it, but it definitely falls short of the marketing.
Inexpensive: Most casual users can find a good pair of headphones for between $20 and $50. Headphones in this price range sound great, include key features like an in-line microphone, and often support wireless Bluetooth connections. If you’re looking for a reliable set of headphones and you don’t need much more than audio, you don’t need to spend more than $50.
That amp, if in good working condition, has 100 times the potential sound quality that those 2 headphones can play. You could improve the sound somewhat with a careful EQ, since the Marantz will have power reserve to spare. But I’d try to find a better headphone, and there are some bargains out there. If I were suggesting an ortho, I’d say get the lower price Mad Dog, which will give you great audiophile sound with the Marantz.
Passive noise isolation is essentially using the body of the earphone, either over or in the ear, as a passive earplug that simply blocks out sound. The headphone types that provide most attenuation are in-ear canal headphones and closed-back headphones, both circumaural and supra aural. Open-back and earbud headphones provide some passive noise isolation, but much less than the others. Typical closed-back headphones block 8 to 12 dB, and in-ears anywhere from 10 to 15 dB. Some models have been specifically designed for drummers to facilitate the drummer monitoring the recorded sound while reducing sound directly from the drums as much as possible. Such headphones claim to reduce ambient noise by around 25 dB.
A. Near-field communication, better known as NFC, is a wireless connectivity protocol similar to Bluetooth. NFC uses less power than Bluetooth and is faster when pairing devices, but it only has a range of about four inches. Some headphones use NFC technology to drive the process of pairing headphones with smartphones, but because of the range, it’s not used to transmit sound. While both Android phones and iPhones include NFC chips, it’s not accessible in Apple devices, so if you want a pair of headphones with NFC, you’ll need to own an Android phone to take advantage of the faster pairing.
Although some headphones available are wired, many more are available that are wireless, and use Bluetooth to enable your music to be heard, even if the stereo or other device is several feet or even a few rooms away. Wired headphones deliver superior sound quality to wireless and Bluetooth because there's no chance of picking up interference from other devices, which sometimes happens with wireless headphones. In addition, wired headphones have no batteries to power them, so there's no chance of interruption should the batteries wear out.