The HD580 + HD300 bass is almost too much for me (midbass really) after listening to the more natural bass of the Omega 2.
Also you're not supposed to be having fun when listening to music, bad Monkey!
Yup Headroom might even have a balanced stock cable version of the HD800.
This is the impedance curve of the HD800 vs HD650, you might need active amplification with the HD800
It will come down to which one you like more Omega 2 or HD800? You can build very nice systems around both of them.
Personally I would get the Omega 2 with either a KGSS or 717 since I know those combinations sound good then go with whatever source you wanted. The Exstata sounds like a good amp too.