[414353]

   
The HD598 is a tad more balanced and clear, but these low impedance headphones are not a good match for a receiver.
 
Most of the times, the headphone jack present on receivers has a really high output impedance, when you plug a low impedance headphone like yours (or HD598) the frequency response (ie, the sound) of the headphone is altered, there's a boost in the mid-bass that also appears less controlled or even boomy.
 
Little DAC/Amp like the Schiit Fulla or Fiio E10K are perfect match for this kind of headphones.
 
In my experience, the Beyerdynamic DT880/250 is one of the best headphones to plug into recivers with high output impedance.

While I don't concern myself with all the impedance and diodes and such of headphones, you make an interesting point I had not thought of.
That is the sound being altered by what I'm plugging into.
However, with my 518s, boominess is not my issue. If they were boomy I would have thrown them in the trash long ago.
I have tried my 518s with several Dac/Amps and the only one that showed any improvement was the Oppo HA1, but that is a ridiculous amount of money for someone like me that rarely uses headphones.
The Schiit Fulla and Fiio are designed for laptops which I do not use.
 Oh, I think it might help to state that my listening is with Vinyl and CD predominately. (I don't like files personally).

 

[414353]

   
You have many high end audio dealers with quality cans available for listening in So Cal.  We even have some here in "little" Austin.  You just have to take some time and look for them.
 
Meanwhile start with your local Guitar Center.

I've looked and I am not traveling 50 miles to Los Angeles for any reason. Guitar center does not carry home use headphones. I've called the two locations near me.
I have only one high-end dealer near me and he does not carry headphones of any type. I know of one other somewhat near my work and they also do not carry headphones.
I'll google, but I don't think there are any others around me.

 

[414353]

I found one other dealer in Anaheim. Unfortunately, they do not carry headphones.

 

[414353]

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[cel4145]

I've RMA'd headphones to Amazon and B&H Photo just because I didn't like them. Amazon has never charged me restock fees (I don't remember B&H doing so either).

Sure. You have to pay the return shipping, but that's a reasonable in home demo fee. You pay their shipping cost if you use UPS labels from them, so not normally too bad. Usually about $10 or $12, in my experience. And since the headphones are generally cheaper than you can buy in stores, usually works out OK to demo a couple.

Anyway, this is the state of headphone buying. If you can't find them in a store to demo or go to a Head-Fi meet, that's about your only option.

 

[414353]

I've RMA'd headphones to Amazon and B&H Photo just because I didn't like them. Amazon has never charged me restock fees (I don't remember B&H doing so either).

Sure. You have to pay the return shipping, but that's a reasonable in home demo fee. You pay their shipping cost if you use UPS labels from them, so not normally too bad. Usually about $10 or $12, in my experience. And since the headphones are generally cheaper than you can buy in stores, usually works out OK to demo a couple.

Anyway, this is the state of headphone buying. If you can't find them in a store to demo or go to a Head-Fi meet, that's about your only option.

 
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[Me x3]

  I've been at this for several months actually and it is the most frustrating thing ever! $10 or $12 to ship back two sets of cans is not bad, but it's all the hassle as well. 
Then there is the whole principle: Everything else one can go to a shop or dealer or whatever, take a look, try it and the purchase, simple. Why not headphones? I don't get it.
 Like I said, I've given up, not worth the hassle anymore.
 
Thanks.

 
You can always get the Takstar Hi-2050 which is only 49 dollars + free shipping (amazon)
It's well built, comfortable, and more detailed than HD518.