Which headphone amp?

Alright man. Well I would say using the hd 800's kinda saves your amp testing for performance results, rather makes your test looking more credible than limp. Dave, I tell ya if all class A amps and all DACS all sound exactly the same to those ears of yours no matter what headphone or speakers you use, than you my friend are looking at a very easy way out from the upgrade bug.  

I am glad you are content and very happy with what you have and you should be. I wish I could say I was done and had an end game sound chain, but I know that I don't...I am getting close though. 

You're right, as is Guldbamsen, the amp rabbit hole can go very deep indeed. Here's a consideration, though. the idea behind a good amp is to reproduce the sound quality of an instrument, or group of instruments, as faithfully as possible - "as if you were there on stage". Now, my modular has 14 oscillators pushing waveforms out into God knows how many voltage controlled amps as possible (ten, I think). The output is 0-10v and this goes through a number of attenuators and output modules into a mixing desk and from there to the PA. VCA design on synths is pretty basic, to be honest. The oscillators tend to be well designed but the voltage controlled amps are pretty low quality. This is just the nature of the beast, VCA's tend to be overlooked by designers. It's vital that a VCO stays in tune and tracks over several octaves (the setup for VCO octave scaling is a nightmare) but VCA's tend to be very simple designs. Yes, you'll use poly capacitors, ferrite beads and electrolytic caps on the inputs to reduce hum, but at the end of the day, you'll get as much line noise as a standard guitar pedal. 

Some synth filters are notorious for having a high noise base - the Korg MS20 / Steiner Parker filter is just one example. Ladder filters (either transistor (Moog) or diode) naturally distort due to their design. 

The same applies to bassists, guitarists, anyone playing an instrument. The quality of the pickups, strings, pedals, amps, PA etc all come into the equation. 

By the same token, you're playing in a live environment and this means that you'll have to factor in distortion from that environment, with sound waves bouncing off walls. Bring in a bassist or guitarist with a few pedals, there's line noise again. 

Perhaps the end of the headphone amp rabbit hole is that you can only reproduce what sounds the musicians are making, and they're never going to make a sound which is acoustically perfect. Then - with recorded sound, the skill of the person recording, mixing and mastering comes into play.

I always think, when mixing or mastering recordings - "make it sound like the listener is on stage with you". So, a headphone amp is going to be one small component in this. It helps if the component works well, but the whole thing works at the efficiency of the least efficient component, of course. 

Just my $0.02c. Back to the soldering. ;-)

Curious . did you listen at a louder volume? I find most amps (even my Burson a bit) loses some composure when pushed to about 90 db. Good solid state amps will keep their composure and resolve at louder volumes. 

I feel the headphones you used are great for amp testing . the sensitivity is huge at 103 db I believe for the 800's and the he 6's are so resistive so you need great amps to drive them properly. 

So my friend my only question is how loud were you listening? 

Some of this is true and to reduce the hotbed of distortion really class A/B design would be ideal to limit it to its lowest possible output. 

Dave . I really do not want to think you are done and that you are chewing on red bills as if you were popping them like Prozac .

Power amplification differences and performances are very real . If an amp cost 500 dollars as opposed to 5,000 dollars there is a big reason for that and not just performance alone . Dave, this hobby of ours is quite wonderful and the diversity is very real. Don't sell the amp section with in a sound chain short. 

Just let your ears do the believing. If you can try out some higher end amps you will see what I mean .

Amps are tricky busines . even down to the quality of resisters, capacitors and transformers (toriodal or not) matters! Just trust me. 

The rabbit hole goes far deeper my friend. 

What did you end up deciding or getting for the 400i amp wise? 

Have you considered portable tube amplifiers. They carry a very rich and warm tonality to them. Seriously, listening to the likes of black sabbath through a tube amp is an experience that is second to none .