I'm waiting on my Vamp Verza, I actually ordered it a month ago but still didn't get it delivered (apparently V-Moda were overworked with the launch of XS, hopefully it'll get here ASAP). I heard it's strong enough for the HD650, I can write some impressions once I get it.
FWIW, I've owned the Vamp Verza for a couple weeks now. Mostly use it with Etymotic ER-4PT IEMs but found that it seems to support the HD650s to my satisfaction at this point. That said, the Verza is simply to hold me over until my Centrance Hifi-M8 arrives. However, I'm looking forward to reading your impressions, as I can't say I have another portable AMP/DAC to fairly compare with yet.