[PurpleAngel]

So what happens when a set of headphones isn't driven properly? Is the issue just in volume as it relates to distortion, or does it also significantly affect soundstage and frequency balance?
Interesting. Are the 250-ohm different in that regard? Most reviews say people prefer 880s, unless they want the 580 signature.

Not sure there is one clear answer for what headphones sound like when not driven properly.
Normally the DT880 provides a well balanced sound, slightly on the bright side, does it sound this way to you?
You could try this cable (Hosa CMP-153), to connect the 18i8's line-output, to the line input on the E7, see how that sounds.
https://www.sweetwater.com/store/de...53-3-foot-3.5mm-trs-to-dual-1-4-inch-ts-cable

The DT880 250 and DT880 600 sound very close, the 600-Ohm sounding slightly better.

 

[S3nsoryDeprivati0n]

It just dawned on me that the 18i8's headphone amp/DAC quality may be the issue in and of itself, rather than one headphone or another not being driven properly. The 770s and 880s sound rather similar out of the 18i8 -- in short, okay. It's a 1st gen 18i8, for the record.

I know the E7 isn't powerful, but since I already have it -- would adding an E9 as the amp solve the issue? Is the DAC of the E7 at least decent?

Probably decent: the iBasso D10, the Headstage USB DAC, and the Pico DAC are all using the Wolfson chip for the D/A conversion. The WM8740 is the only chip converting from a digital signal to analog sound in all of these DAC's.

 

[PurpleAngel]

It just dawned on me that the 18i8's headphone amp/DAC quality may be the issue in and of itself, rather than one headphone or another not being driven properly. The 770s and 880s sound rather similar out of the 18i8 -- in short, okay. It's a 1st gen 18i8, for the record.
I know the E7 isn't powerful, but since I already have it -- would adding an E9 as the amp solve the issue? Is the DAC of the E7 at least decent?

An Audio Interface is going to be used by someone in Audio Production (creation, mixing editing), so chances are that person would have a slightly better ear, for audio quality, over the average person. So the Audio interface needs to have fairly good audio quality or it's going to be returned to seller.

Do you by chance have access to a receiver, receivers seem to do a decent job of driving high impedance headphones.
If the DT880 sound better plugged into a receiver, then you know the 18i8 is not driving (amplifying) the DT880 well enough.
Try the DT770 plugged into a receiver.

 

[ProtegeManiac]

For reference I own DT880/600's and DT770/32's. Also have a FiioE7.

So as far as I understand, the E7 will only act as a DAC if plugged in via USB, and works as an amp via line-input.

Partly true. If you're using USB input and headphone output though then both the DAC and the headphone amp circuit are working.

1. Using the E7 with my DT770s out of an LG G6, the soundstage seems to open up somewhat and it overall sounds clearer. Is the amp itself responsible for this, or is it just placebo?

Higher quantity and quality (ie low distortion) power out of the E7 combined with better channel separation (AFAIK the E07K is in the low 90dB range; smartphones, including Quad DAC phones, are at around 70dB or lower in some cases) are likely making for that difference, although if you control for effective dB output at 1000hz, up to a point it can be hard to distinguish.

2. I'm wondering if my 880s aren't being driven well enough by my Scarlett 18i8 (rated by Focusrite for 250ohm headphones), as the 770s sound better in all honesty. Does pairing the E7 with the 18i8 solve this problem? I don't know if the headphone amp or the DAC is the issue in the 18i8 (I would imagine the amp).

That interface has a bit of an issue with both. Its output impedance is too high for the DT770, and while it has more power, it has more distortion from lowered damping factor. Part of what you think is better drive is actually the amp having less control over the driver, ie, louder (but less controlled bass), whereas it might lack power to drive the DT880 given its 600ohms but it also doesn't struggle to control the driver movement at that output level.

Think of the first like if you took a bone stock 1990s Mustang, put Prius wheels and rubber on it, and drove it around a track; the second is more like buying a good German sport sedan albeit with the entry level 4cyl engine but you went for the 19in wheels and sport tyre package.

3. Conceptually, what contributes to volume and what contributes to quality, or do both contribute? Obviously an amp contributes primarily to volume, but does it also contribute to overall quality (i.e. frequency balance, soundstage, lack of distortion, etc)? If the amp doesn't contribute to quality, is there any point to using the 770 32's E7 with a smartphone if all it's doing is amping it and the DAC isn't being used (considering I get max desired volume levels at about 80% of smartphone volume)?

Output volume is determined by power quantity and gain. The quality of the sound is determined by channel separation and distortion levels, however in some cases some people perceive higher distortion levels as better than lower overall distortion levels but distort in a different way, like the difference between an objectively bad tube amp that is less amp and more "warmifying boombasticator" and an honest albeit slightly critical but otherwise really good solid state amplifier.