Thanks for info kamikazi & Hi-Phibian; greatly appreciated! I'll put them on my list of contenders

I'm still keen on the Asus Xonar Essence One tho; if the price is more sane than R.10k, and it can drive the Sennheiser HD 650's via the balanced XLR out's, then it gives me more do$h to spend on proper cables.
Anyhowz...
I was in a hurry to get the headphones, so I arranged with the reseller [DJMix] to allow me to collect today... and so I did

The Sennheiser HD 650's are
AwEsOmE!!! Even tho it's running from my PC's onboard analogue audio out to the Samson Audio CQUE8 Headphone Amplifier, without any special cables [some random male-to-male 3.5mm stereo jack cable into an another random 3.5mm to 1.4 stereo jack adapter]
Thinking about getting a better cable over the weekend, tho I doubt I'd get much benefit with that using the PC's onboard analogue audio out.
Been listening to a variety of songs, from Crosby, Stills & Nash to just Neil Young, to Buckethead, to The Flower Duet [Lakme], to Audioslave, to Pearl Jam, to RATM, to Metallica, to Led Zeppelin, to Van Morrison, to Dream Theater, to Charlie Parker, to Charlie Hunter, to Joe Satriani, to Albert King, to Robert Johnson, to.. to... too many others
And I'm stocked!! Wonder how more amazing it would sound with a proper DAC/AMP...