The same happened to me and I decided to keep it anyway. I just gave my on line retailer a 4 stars instead of a 5 because of the screen halo.

Agreed. Power for H650 with 1V voltage as an example: U=1[V] R=300[Ohms] P=Power in Watts[W] P=(U^2)/R=1/300=0.0033333[W]=3.33[mW]   Power for K712 with 1V voltage as an example: U=1[V] R=60[Ohms] P=Power in Watts[W] P=(U^2)/R=1/60=0.01666666[W]=16.66[mW] It is a power 5 times bigger...

My K712( Made in Slovakia) bought 2 weeks ago at: https://www.brack.ch/akg-k712-pro-487908

Agreed, and after reaching 70hours, I confirm the quality. The bass is not boosted but extended. After 70 hours(14hours each day) it is as good if not better than my beloved HD650.  Fresh from the box it sounded flat and the bass like something was missing. My HD650 has had no change from day...

My X5II is using 2x200GB at this moment (all my collection in FLAC) My Xduo X3 is using 2x200GB I do not upload the collection database. I use directories Artist name/ albums to navigate into my collection.

The X6 we talk about is a DAC/ Headphone amplifier capable of delivering from 90mW/600 Ohms up to 1W/16 Ohms. You can if you choose to, use it to feed small speakers instead of your headphones. If you need more power you need a bigger amp.

I have no problem driving my HD650 with the FiiO K5 ( specs: 150mW/300 Ohms). The FX Audio X6 is given at 180mW/ 300 Ohms. According to the specs it is OK. I have ordered the X6 for that very reason.

Quote:     HD 650->300 Ohms -> 180 mW with 24 mA K712->62 Ohms-> 180 mW  with 54mA  ( more than twice the current to  get the same 180mW)  Use I^2=P/R-> sqroot(P/R)=I I is current P is Power R is load impedance