Just wanted to chime in here to hopefully provide some additional insight. There are significant differences between ZO and other headphones amps, and unfortunately, explaining these differences will warrant a fairly long post. But since I know this explanation hasn't been provided anywhere else, I thought it would be a good opportunity to start posting this kind info for everyone to read.
Headphone amps are first and foremost designed to increase the volume level output, while at the same time, maintain sound quality. However, as RPG mentioned, all amps will modify the sound in some way or another. But the key point to remember here is that their purpose is not to improve SQ, but to ensure there is no loss in SQ while the audio is being amplified (I have a feeling some may disagree w/this statement, but I'm referring to the technical, not perceptual aspects). Now, some headphone amps (such as the E11), have built-in bass boosts, which when activated, do two main things:
- It provides a "bump" in bass levels at a single, dedicated frequency (e.g., regardless of which level of bass boost is selected, the img below shows that the e11 only emphasizes the +/- 50Hz frequency). Unfortunately, all headphones respond to bass in different ways, depending on how they were tuned by the manufacturer (among other things). So although bass boosts can adjust bass intensities, they can't be adjusted to match the specific characteristics of your headphone (or your listening preferences for that matter).
- In order to increase the bass intensity/levels, traditional bass boosts have to redirect power from the highs to the lows when its activated (i.e., when boost is off, it has a flat response - no SQ loss; but, when turned on, frequencies >400Hz dip below 0dB). This will not only result in high-frequency SQ loss, but can also cause the bass to sound muddy or overpowering.
ZO offers more advantages than just being a headphone amplifier. First, its "bass boost", is implemented in an entirely different way, which resolves the issues found w/traditional bass boosts. The img below shows 12 out of the 32 available profiles for adjusting the bass intensity. If you'll notice, as the profiles go from green to red, the max bass intensity not only increases, but the frequency of emphasis (frequency that corresponds to that profile's max bass intensity) gets shifted downwards. This is important b/c as frequencies get lower, significantly more power is required to accommodate for headphone/speaker inefficiencies, as well as your own ear's insensitivities.
This entirely unique method of bass adjustment not only allows you to increase/decrease the bass intensity, but also provides you with a quick and easy way to customize ZO's sound signature to match the sound characteristics of your headphones. Although it would not be appropriate for me to say whether or not the ZO pairs well with the m80s, I would like to emphasize the fact that ZO provides the largest amount of flexibility for finding just the perfect amount of bass (from no bass enhancement, to extreme levels), regardless of what gear you use, what you're listening to, or what your personal sound preferences are.
ZO also resolves the second issue w/bass boost discussed above, by ensuring there is no loss in the mid- and high-frequency ranges, regardless of which profile you decide to use. There are other aspects of ZO's bass enhancement circuity that works to help control and prevent speaker distortion, but for the sake of brevity, I will not go into detail here. If you want to find out more, I recommend visiting the ZO product page and the tech page on our site.
I would also like to remind everyone that we offer a 60-day no-hassle return policy for purchases made directly through digiZoid. =)