Try it out first with the HE-500, if you like it, then keep it. I would still keep the O2. While the O2 isn't the best match for these planars, the O2 is still a great amp for most dynamic. For example D2000 off an O2 is very, very clean and fast. Not quite the LCD-2 or HE-500 performance but still very enjoyable
Also, cheap speaker amp would be the best at that price. Look for vintage amps without around 20-50Watts of power. I always see vintage Marantz somewhere for good prices.
iam totaly new when it comes to speaker amp.... but isnt speaker amp quite big ? i want it to be on my computer desk, thats why i wanted to ask about Audio GD NFB 11.32 or modi/magni.
And iam thinking of only own 1 pair of headphones :p