Taking the amplifier and plugging it into different sources, I'd say the resulting sound is clean. This means the audio is dependant on source, both for signal-strength, but also for signal-quality. It doesn't seem color the signature in any noticeable way. The transparency the amp features makes it ideal for pretty much every genre of music.
Using it with headphones like SoundMAGIC's HP150, BrainWavz's HM5, and Philips' Fidelio L2 the EB03/EB01 combo shines, amplifying the sound without coloring it; improving soundstage, imaging and dynamics. However, when paired with Sennheiser HD600, it brings the volume to a loud listening level, but it loses some dynamics.
What about noise?
At normal listening level, the noise floor is below audible levels, and you will not hear anything. At higher levels and with sensitive headphones, there is a sliver of background hiss of background noise, but it's not enough to make me reconsider the offering.
EB01-E with EB03
When reviewing the EB01-E I said the signature needed some amplification since the signal wasn't strong enough on its own. With EB03, the signature dramatically improves. The bass becomes tighter, mids gain texture and the treble is sparkly (though it heats up even further and would cause listening fatigue in time).
The "intimate" soundstage also expands a lot, with better instrumental separation, and a much wider & deeper stage overall. EB01-E was no match for iFi DAC on its own, but with the amp attached to it, it finally catches up. In a way, this proves how the two devices are designed to work together.
I felt the need to dedicate a lines on portability. Though EB01-E and EB03 are large and seem to be limited for home use, they're still very light. When I opened EB03, there was a lot of space inside.Therefore, I could say the combo is not necessarily portable, but it is transportable, a helluva lot more than ASUS' Xonar Essence One. It most assuredly isn't on the level of Fiio's portable amps, but it can be put in a backpack and used alongside a laptop.
The external 15-20VAC adapter hampers its portability, but other than that, this is a light device placed in a bulky casing. It could be a lot smaller and more portable than it actually is.