I'm sorry for being the Curious George of this thread, but I have another question in regard to driving HE-6 with speaker amps.

1. When listening to headphones via headphone amps, one thing to consider is the output impedance of the amp in relation to the headphone's load impedance, i.e. damping factor. While the actual formula is complicated, a general rule of thumb is that headphone's load impedance divided by the amp's output impedance should be greater than 8, or there could be distortion in sound due to poor damping factor. This explains why high-impedance headphones generally perform better with OTL tube amps (which have high output impedance) compared to low impedance headphones. The HE-6 is 50 ohms, so in theory, the amp's output impedance should be less than 50/8 = 6.25 ohm.

But what about speaker amps?

While many headphone amp companies provide info on output impedance, I'm not so sure about speaker amps. I have several theories, so I hope an expert could clarify things regarding this matter.

Theory #1) Due to the different nature of speakers and speaker amps, damping factor is not an issue at all. Either a completely different formula is implemented for speakers, or poor damping factor doesn't cause distortions.

Theory #2) Since speakers generally have lower impedance (4-8 ohms) than headphones, most speaker amps are designed to have a very low output impedance (less than 1 ohm). Therefore, driving headphones with speaker amps will almost always result in a sufficient damping factor.

Theory #3) Speaker amps can have high output impedance, especially if they are tube amps (tube headphone amps have higher output impedance than solid-state headphone amps). Therefore, with a low impedance headphone like HE-6, it is more beneficial to use a solid state amp with low output impedance, purely in terms of damping factor.

Of course, all these theories could be wrong. Anyone who can explain things correctly will be much appreciated.

2. Also, unlike many folks out there, I'm using an HE-Adapter between the HE-6 and my speaker amp. In this case, will different rules apply in terms of output impedance and damping factor, compared to connecting the HE-6 directly to speaker amp? Or is there theoretically no difference in output impedance and damping factor whether I use a HE-Adapter or not?