KITTYAudio g-d NFB-28.38 http://www.audio-gd.com/Pro/Headphoneamp/NFB28.38/NFB28.38EN.htm
I have a NFB-11.28 and it's amazing. The 28.38 is even better and is also balanced.
It is my first purchase and I love it, I also have not tried out any other (balanced) amps , so my opinion on this matter is severely biased and not based on any comprehensive testing and comparing.
Also my HD6xx has yet to arrive ...
You did say "any recommendation". ;)
KITTYFor a Balanced 4pin XLR cable you can look on Ebay and see if you can still find one selling from Corpse Cable, they're reasonably priced and uses the original HD 650 cable, so there should be no problems in terms of quality.
As for a balanced amp, I'd say go for the Schiit Jotunheim (Amp only) and you should be set. If you need a DAC then you can either get the DAC module ("audiophiles" don't seem to like it much but I feel it's good enough) or you can use another external DAC of choice. It's one of the better balanced Amps for the price range ($399 for the amp itself), and it has more than enough power to drive your cans.