The lyr is a very good amp and pairs well with the 650...very well. But consider that the lyr runs $475 shipped and you MuST roll in a decent set of tubes that will go about $50, so $525. If you are willing to build the crack kit or have someone build it for you, you can get a better pairing for less. Kit =$300 shipped plus the Tung sol 5998 will run about $375. That's an amazing deal when you consider the places it will take the 650.
Both amps are very good choices and my two personal favorites.
The lyr is built like a tank with no maintanence required and has the option to roll in some nice tubes to flavor the sound to your liking. The lyr will also do a great job with other hp's especially planar mags.
The Crack is special though and seems like it may have been build exclusively for the 650. IMO it is a clearly and appreciable better choice for the 650. But it will not have the flexibility to drive other hp's, especially planar mags, like the lyr.
At first, I actually wanted to try the BHC, but knowing that it mainly just shined with Senns and Beyers , I thought the price was a tad to high, unless you build it yourself.
Then I found that the Mad Ear , with the right tube was just beautiful with the HD650.