^^ Congrats and glad to hear that you've been enjoying them. My experience is that you'll hear some improvement as well after they get past 100 hours or so..ymmv. But for sure, these hp's response very well and scale up with better gear. The uberfrost is a very nice upgrade and it's where I ended up.
And for the amp, I spend A LOT of time with the Asgard2 and the hd650. It's a good combo. The A2 offer nice clean resolving power that compliments the 650 well. But...if you want to truly have a religious experience you'll have to try the 650 with the Crack amp. It's a match made in heaven. IMO
I denied the 650 for years because of the reviews about being veiled and slow. Wrong. Then I denied the crack for years also because I'm not that much of a diy guy when it comes to building amps. My advice, if you don't want to build it then ask someone to build it for you. There are a great community of very handy people who would offer to do it for nearly a song.
I've been serious about quality audio for 20 years. The ONLY setup that I've heard that floored me more than the crack/650 was the Stax sr/007 mkii and the Blue Hawaii. That's it period.