I have posted the following elsewhere around Head-Fi, but I'll repeat it here.
What opened up the SQ of the HD800 for me was a better DAC.
Specifically the multi-bit upgrade to my Schiit Gungnir D/S.
It was like turning on the "great sound" switch.
I've stayed with the Gumby DAC (now with the A2 and Gen5 USB) to this day.
The best I ever heard the HD800 sound was at a HP meet here in Nashville.
Dan Clark of Mr. Speakers was here with his rigs: Schiit Yggdrasil and two amps: 1) Ragnarok and 2) Woo-Audio WA5.
The HD800 sounded great with the Ragnarok, but with the WA5 the sound was over the top good (it's a $5,000+ amp).
The warmer tube sound of the WA5 took away some of the brightness of the Yggy and the HD800.
Net, the HD800 scale as well as, or better, than any other HP that I've heard. When you get it right ... it's magical.
It's not possible to see your gear
@allhifi as you don't have a profile set-up - we may be able to help you more.
As for the price, (I believe) the HD800 are no longer made new by Sennheiser.
They were replaced by the HD800S and HD820 (neither of which are close to the original HD800, for me).
So it may be possible to buy new, or certainly used, HD800 for ~$800.
Mine were ~$1,500 new and worth every penny
Cheers, friends.
RCB