Thanks for reply. I haven't try direct connection yet (becouse I'm still insecure).
I can buy sth from this shop:
I was thinking about Duelund 10R10W or Mills MRA-12 8R2 or 15R for parallel resistor. But as far as I'm concerned in my situation (powerfull solid state amplifier) resisitor in series would more important to protect my HP. What other values it might have than original 25 Ohm 1/4W to still protect my headphones?
And how solid state amplifier would react to such high impedance (aprox. 50 Ohm) without big (for example 10W from additional parallel resistror) load (amplifier will be for example very warm?) If I connect he500 directly to taps?
What would be sympthoms of "overpowering" my headhones if I use them without any resistors protection? Headphones will play probably very loud on lower volume levels but when I will know if it's to much for them before they will be damaged (will any distortion in sound appear first)?