If the HD-650 is too dark for you as it is, why pair it with a warm amp? The Lyr is fairly warm right?
The Magni and ODAC are perfect for the HD-650. People say they're bright, but they're really not. Despite that they still do sound best with warm headphones.
The only way I'd suggest a new cable is making one yourself. Try a low capacitance wire such as Belden 1192A (dirt cheap) or similar. There's a good reason people use silver with the HD-650, but I don't go there..
I prefer stock cable for the HD-650. My belief is that the capacitance of the wire changes the tone of a headphone slightly, but not enough to be measurable. It's kind of like warm/cold amps that measure the same and have very good measurements too.
Thanks a lot for your input. Don't get me wrong, I really think the warmth is amazing even on tube amps. You do have a good point of going for a brighter amp like the magni. Initially I was worried it might get too bright which is why I asked how the Lyr handles the HD650. Seems like a mix where it retains some of the tubes warmth but not so far in as other tube amps. Of course I'm looking at other options. If certain amps like the Magni isn't too bright I would definitely give that some consideration. To begin with though, this is just all thinking for now. Not buying any new equipment until I feel comfortable doing so :P