Underpowering headphones isn't about volume level. They can get very loud, but they won't sound their best. There's just not enough power to let the drivers function as designed. DACs and amps do change the sound of headphones, and it's not an issue of neutrality, but presentation as a whole. Underpowering headphones can make their desirable traits turn into the opposite. As an example, the HD 6XX sound stuffy and dead on the DACport HD on low gain, simply due to being high impedance and requiring more power. Amps deliver different levels of power according to impedance. The HD 6XX are plenty sensitive to make decent sound with little power, but that won't yield their best performance. The drivers have an impedance of 300 ohm, but that number is frequency-dependent and can increase much higher as music plays. However, once the DACport HD is set to high gain, the HD 6XX are totally transformed to the point that they sound like different headphones, because electrically, they're functioning according to their design. The bass gets tighter, the mid-bass no longer bleeds into the mids, *and the highs get sharper and smoother with much less "grain". The separation and layering increases, and also the width and depth of the stereo image. It's the same DAC/amp, but the power delivery increased, so the drivers are behaving in a different, optimal way. You said you know you're underpowering the HD 6XX, that it gets loud enough, and that you don't think the sound signature will be altered by the DAC and amp. If you don't have hearing damage, you will instantly hear the enormous change with the DACport HD on high gain. You will even be able to enjoy them at a *higher volume comfortably, because clean power yields less distortion. It's not an opinion of mine, but just plain science. 😎👍 *typo edits

Thanks for the info! I switched from the 32 Ω DT 770 Pro to HD6XX because I can't tolerate the sibilance and the high frequency peaks produced by it. The DT 770 Pro's mids are recessed but it is bearable when compared to its highs. Its mid-bass and sub-bass are deep, clean, and tight despite many people complained the bass is overwhelming on the DT 770 Pro. Perhaps they are referring to the 80Ω version? On the other hand, the high frequencies produced by the HD 6XX are detailed and smooth and I don't find them to be "veiled" or "rolled-off" like others said. The mids on the HD6xx are good and the sound stage is fine but not really better than the closed-back 770 Pros. However, the mid-bass frequencies of the HD 6XX are very bloated, muddy, overly punchy, and leaks into the mids. It seems like my impression of these two headphones are different from others. I'd admit I am driving the HD6XX directly with my laptops and smartphones. I know it's under-powered, but the volume is loud enough for me and I don't think DACs and Amps will alter the sound signature. In fact, they shouldn't as they are supposed to sound as neutral as possible. I've purchased the DACport HD and let's see how it works out.

Hey, if we have a toy in the mail running late, that means we still got it good despite all the bad stuff going on. We gotta be grateful. I thank God for everything, and I live in Puerto Rico, which is going through a lot of corruption in the government right now. As long as I have a roof over my head, food, water, and electricity (and my toys), I'm good! 😁