I'd like to think that's the case as well. But then you were takling about gain and volume.
To illustrate, a 1x gain at 2vrms of input will sound louder than a 2x gain at 0.75Vrms of input.
Gain alone will not tell you how loud the volume will be or if the amp can properly drive a phone. You need the input level and max power the amp can supply given a specific load in ohms.
An amp may have plenty of power for a given phone. But if gain is not properly match, the headphone will sound underpowered or may clip.
But it's always true that higher gain has higher noise. Digital volume works best at higher volume level and analog pots are prone to channel imbalance at very low volume setting. Which in all cases you want to avoid a higher gain if possible.
Okay, let me see if I understand you correctly (because I'm only on page 533 of this thread in real-time). Let's say I have my DX90 set on low gain, and I'm using the volume of my DX90 to raise the volume. It's not going to drive the HD800s. But if I use my external amp (on low gain) with my DX90 on low gain, as described above, and I'm using the volume on both devices to hit a comfortable volume level, then in theory, somewhere in the middle I should hit the sweet spot, without adding any extraneous noise, yes? That is to say, I've kept the noise level very low on both devices, but achieved sufficient volume to drive the cans, assuming my amp is up to the task. Is this correct?
But hey, so far I've only updated the FW to Lurker's latest version; and my DX90 is sitting - out of my line of sight - with burn in sounds going through it for the next few days before I can even reach the listening point.
In the meantime I think I'll ruminate on what to load up in the DX90, first. I'm thinking Neil Young's "After the Gold Rush," Metallica's "Master of Puppets" (Steve Hoffman's master), Pink Floyd's "The Final Cut," aaaaand...wow, I need some hi rez in there. Duh! Jimi Hendrix "Electric Ladyland" 23/96 vinyl rip, Yes "Tales of Topographic Oceans" DSD, for trying it out as a desktop DAC. Sorry. Just riffing off ideas of well recorded albums.