I've had my iSine 20 for a while now so I thought I'd post some impressions. For the record, these are only my opinions. At home, my reference headphones are Abyss with a Chord Dave and WA-5LE with Japanese tubes. In noisey environments I use an Audeze LCD-XC with Chord Mojo. I admit I love Rob Watt's DAC designs and am looking forward to the Hugo 2 for headphone listening.
First of all, I completely disagree with those who've said that an ear canal seal with the iSine 20 is a bad idea. These headphone are more forgiving of resonance, etc, because of their semi-open design, but they abosoltuely sound better with a nice, easy seal not to deep in the canal. Better bass, better isolation, better sound, and it's not subtle. Find the right fit for your ear and make a seal. It's just better.
For these I use an iPhone 7 plus as a source, mostly Tidal HiFi and HF Player high bitrate content. I like to start with well-recorded accoustic recordings because I know what they're supposed to sound like and beyond that I use the Abyss as my reference for what is the best possible bass on a headphone (which only sound speaker-like IMO on the Abyss). I don't bother listening to the direct output of the iPhone - just comparing Cipher with Mojo.
Cipher is an engaging sound in a convenient package. I don't like that peak at 4KHz at all, so I've used someone else's EQ settings on this thread to reduce primarily the 4KHz bump and some attenuation a little below and a little above. The bass bump is audible ... it's also not really for me. It adds stuff that's just not there. So, it's a fun sound, but to me it's a bit fatiguing and not as natural and analog/organic as I'm used to. I enjoy it, it's convenient, but you can do better with these headphones.
I admit, I don't like to use EQ. For me the iSine 20 sound spectacular right out of the Chord Mojo. It's much more natural sounding. I'ts got plenty of bass, and quality bass. It can't equal the Abyss in speaker-like bass, and pumping it up artificially doesn't get you there. The Mojo is not only less fatiguing, it's just more realistic on recordings where natural sound is expected. The Mojo itself has a warmer sound, and I'll take the DAVE over it, but it's amazingly good for a form factor of this size.
So - make a seal. The iSines are better with it and I don't understand the obersavtations of those who have written differing opinions.
For me, analog with Mojo is preferable to Cipher all day long. It's more musical and more natural, and just better. In my opinion. That said, I'm perfectly happy to enjoy Cipher and enjoy playing with EQ when I don't bring the Mojo, which honestly is almost never.