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.
Preferences for the length of headphone cables vary for portable users, especially depending on where you prefer to wear your device: a backpack or a pants pocket necessitates a longer cable, while you'll opt for a short one when wearing a player on a neck lavalier or an armband. But a cable length at either extreme need not be a fatal flaw: extension cables can lengthen those that are too short, and cable wraps can tighten up ones that are too long.
Noise cancelation for kids? Doesn’t that mean they’ll ignore their parents even more often than they already do? Perhaps, but it’s a risk worth taking if it means your kids’ hearing will be protected over the long-term. That’s exactly the premise behind the Puro PuroQuiet headphones. Not only are they wireless and great-sounding, but they also come equipped with a software limiter that keeps the volume at or below 85dB, which is considered the maximum volume that children should be exposed to for prolonged periods. The noise-canceling feature means they’ll actually be able to listen to lower (therefore safer) volumes.

Dale: It’s really the same with any genre or sub-genre of music, that the sound from different artists and tracks can vary a lot, so having more than one headphone is a plus. When only one headphone is available at a particular time (portable use especially), one option is to use a headphone that can accommodate a wide range of genres, in which case there may be compromises to consider. Another option is to carry two headphones – one on the head or around the neck and another in a carry case. Some of the small headphones can make this easy to do.
While Apple’s AirPods get a lot of attention for how well they work with other Apple products, there’s actually a more affordable option that’s just as tightly integrated: the Beats BeatsX Earphones. Apple owns the Beats brand, and it’s built the BeatsX earphones with the same W1 chip that’s in the AirPods. That means that the user experience is virtually identical – iOS makes it super easy to pair them with any iPhone or iPad. Our favorite part is they have a Fast Fuel feature, so when your battery is low, plugging them in for five minutes provides two hours of talk time. We’re also big fans of the COWIN E7 Headphones. They’re wireless, they’ve got on-board noise cancellation, and they can last up to 30 hours on a single charge. The E7’s have an impressive spec sheet for any price point, but the fact that they’re so affordable makes them an even better value. If you’re looking for affordable over-the-ear headphones that don’t make any compromises, this is the pair to get.
Once you’ve got that all order, to put a cherry on top it would be ideal for the amp to play nice with my laptops (PC at work, Mac at home) *and* my *iPhone* 4S.  I haven’t found a headunit that works with PCs and iDevices.  If one doesn’t exist it would be a big plus for the amp to include inputs so I can get digital sound out of my iPhone (with the Pure i20 or its ilk) and into my headphones.
I’ve never enjoyed the audio quality of Bluetooth headphones, but that’s just me. The sound is better than it ever has been, and it’ll get you 90% of the way there—but not everybody is willing to make that tradeoff. Since USB-C headphones have largely ceded their market advantages over Bluetooth, we have to examine the consumer audio technology’s performance in a world where the headphone jack is disappearing.
Sensitivity is a measure of how effectively an earpiece converts an incoming electrical signal into an audible sound. It thus indicates how loud the headphones are for a given electrical drive level. It can be measured in decibels of sound pressure level per milliwatt (dB (SPL)/mW) or decibels of sound pressure level per volt (dB (SPL) / V).[12] Unfortunately, both definitions are widely used, often interchangeably. As the output voltage (but not power) of a headphone amplifier is essentially constant for most common headphones, dB/mW is often more useful if converted into dB/V using Ohm's law:
Ok, it’s been a month and a lot of new experience. I’ve auditoned ATH M-50 (clamp’s too tight; they sweat my ears just from few minutes of exposure) and Senn HD 600 (the velour pad is amazingly comfortable & size is ok). So, long story short, now I can refine my search to: circumaural&non-pleather/foam pads, which brought me to Senn HD 439 (cloth) & 518 (velour).
I’ve had only a few minutes one day with a 598, so I can’t say exactly. But since the HP100 is closed and the 598 is open, I would get the 598, as long as open back is OK for you. I don’t think you can go wrong with the 598 in any case – it’s a very good headphone. Watch carefully for any cracks to develop though, since there were many reports of that.
These headphones pack about 16 hours of battery life, which ought to be enough for a whole day or more, but if not, there’s always the option of using an analog cable instead. An external switch lets you turn the noise cancellation on and off. Make no mistake, these might be aimed at kids, but the quality of construction, selection of materials, and color choices give them an appearance that will still appeal to your young charges long after they’ve outgrown their Disney phase (some of us still haven’t).

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.