IEMs/Headphones Pair up.
The sound of any source, either if it is a DAP, DAC/amp, or a portable usb DAC/amp dongle, is based on pair up synergy with different earphones and headphones. Afterall, you are hearing the sound of earphones/headphones connected to the Source. In this section of my review, I will go over how various earphones and headphones pair up with RU6, and mention volume setting (v) and gain setting (High Gain or Low Gain). All connections were balanced, except for R70x. RU6 was connected to my Galaxy phone with volume set at the max (on the phone), and I was using HibyMusic app.
Oriolus Traillii (v29, HG) – dynamic natural full-bodied tonality with a balanced sound sig; great retrieval of details; punchy deep bass, natural detailed mids, treble with a good definition and natural sparkle; very wide soundstage expansion with holographic imaging; black background. No issues with hissing in high gain.
UM Mest MKII (v30, HG) – this one was a bit of a surprise since with these iems I’m used to a mildly U-shaped sound sig while here it sounded quite balanced. Bass hits strong with a great authority, and I hear a deep sub-bass rumble; mids/vocals are clear and detailed, a bit more revealing; treble is crisp and clear, on a brighter side but with zero fatigue. Soundstage is very big and so does imaging, creating 3D holographic effect. No hissing here. In this pair up the sound is a little more revealing, but still great!
Empire Ears Odin (v29, HG) – very balanced sound sig with a naturally revealing tonality. Bass has a deep sub-bass rumble and tight mid-bass punch, both above neutral level. Mids are very detailed, layered, revealing but not too bright or sterile, actually with a good level of neutral body (I recall from my R01 testing, Odin sounded a bit thinner). Treble is crisp and natural, very good non-fatigue extension. Soundstage is wide open and 3D holographic. I hardly noticed any hissing even in high gain.
CFA Solaris 2020 (v24, LG) – right away had to switch to Low Gain due to hissing in HG. In LG, hissing is reduced down to a minimum. The sound has a natural smoother tonality, good bass extension with a textured sub-bass rumble, natural detailed mids, a little peaky lower treble but nothing too harsh, treble has a decent airy extension; soundstage is wide; background is black except for a very mild waterfall hissing.
FiR Audio XE6 (v27, HG) – mildly L-shaped signature with a big bold speaker like bass, thanks to XE6 kinetic bass drivers, smooth natural mids and vocals which are a bit recessed, and natural detailed treble. I was worried that XE6 kinetic bass might lose its power, but it was still hitting strong. There is a very mild waterfall hissing in High gain, which completely goes away in Low gain. I was going back and forth with this one, and in low gain of RU6 the XE6 still sounds very good. Soundstage is big and wide open.
64 Audio U18t (v28, HG) – slightly mid-forward signature due to more neutral bass quantity of U18t, still with a good extension and punch, just closer to neutral in quantity. Mids are clear, transparent, very detailed, and slightly more forward. Treble is very crisp and clear, high definition and zero harshness. U18t does present you with a more forward and more revealing tonality, but in pair up with RU6 it sounds less harsh and a lot less fatigue in comparison to some other sources. Very mild/faint waterfall hissing in high gain, which completely goes away and becomes silent when switching to Low gain.
It’s hard for me to pick the favorite IEM pair up since I enjoyed all of them with RU6.
Beyerdynamic T5p 2nd (v37, HG) – a very natural detailed tonality with a balanced signature. It actually sounded pretty good. Bass could have benefitted from a little boost, but overall, the bass has a deep extension, nice fast punch, mids have more neutral lower mids, clear detailed upper mids and vocals, and detailed crunchy treble with a nice airy sparkle. Adding Cayin C9 amp beefs up the bass a bit with more weight in sub-bass and mid-bass, but even without C9, it was still a great pair up.
Meze Audio Empyrean (v47, HG) – no problem driving Empyrean, though the tonality was a little brighter and more mid-forward in sound presentation, plus bass was lacking some punch. To improve this, I added C9 straight from 4.4mm output of RU6, and was able to regain body in mids of Empyrean and can hear now a deeper sub-bass with more weight in mid-bass.
Audio-Technica ATH R70x (v74, HG) – had to use 3.5mm, the only cable I have with these 470ohm cans, and raised the volume to 74 since these are harder to drive. The sound was more mid-forward with bass lacking some impact. It didn’t sound too bad, but I wasn’t able to drive these headphones to their full potential, and added C9 to the output. That surely improved the sound with deeper sub-bass and beefier mid-bass, more body in mids, and overall, more natural balanced sound.
I don’t have a lot of demanding headphones to draw a definitive conclusion about RU6 pair up. With a few I tried, I felt only Beyer’s T5p 2nd gen was driven to almost its full potential while others were lacking a bit of a weight in bass, which I compensated by adding Cayin C9 tube amp on the output. With easier to drive headphones this shouldn’t be a problem at all, but be aware that with more demanding ones you could have a little more mid-forward sound sig.