I have both headphones. I have had the he 500 for a month. the he 6 for a couple days now. I power them with a schiit lyr. the volume on the lyr is always maxed. i have electro harmonix 6922 tubes. they are inexpensive, good sounding and make no noise at all. dead silent. the volume on my computer goes rarely above 30. it can go to 100. at 30 my skull want to crack. i have heard on this forum people saying that the lyr was not an optimal choice for the he 6. i d'ont know what is an optimal choice, but what i know is that the lyr does an admirable job with this beast of an headphone. i have enough volume room to explode my brain.
i prefer the he 6 and not by a small margin at all. by a huge margin. eventually i will learn more about speaker amplifiers and i will go that route, as many people here have done. i am very tempted by a cary audio sli 80. i love the sound of tube amps. i wanted to buy a smaller tube amp but some people have discouraged me telling me that the amp in question might be underpowered.
Good to hear you prefer the HE6 to the HE500; that's a relief. Knowing just how good the HE500 is that is a real compliment to its big brother. I haven't heard the HE6 yet to be able to compare it to the 500, but I may be able to hear it at a local meet sometime next month.
For the Lyr, if you are using the volume maxed out, it may be best to actually max out the volume for your computer and then control the listening volume with the Lyr. This is the best way to listen to bit-perfect (or as near to it) music with as little degradation as possible.
Oh yeah, once you get into speaker amps it would be interesting to find out how much of a difference there would be between the 500 and the HE6.