Ayre QX-5 vs Lumin vs dCS Bartok

Put MSB Discrete DAC in your list. It has MSRP right under $10K. The second optional power supply is $1,500. The Renderer module about $1,500, and the ProUSB ProISL module combo about $2,000.

I can put in a good word for the Ayre.  I owned the QX-5 Twenty for a while and really enjoyed it.  I found it to be one of those "just works" pieces that never gave me any trouble and always sounded great. I used the network input as a Roon endpoint, the balanced headphone outputs with my Focal Utopia, and the balanced preamp outputs with my Genelec 8030C monitors.

Surprised this thread didn't go further.  I own the AX5/20 (selling as I have the Vandersteen HP5 amps in bound).  I owned the QX5/20 and LOVED it for so many reasons.  Just a great digital hub that sounds great.  The Lumin is also a great DAC and I agree with the first posters answer in the differences. I personally like how 'fast' the Ayre gear is.  It is so revealing.  Whenever I change out and try something else, I realize that over the long haul, I love how detailed and still musical the Ayre gear is.  Personal choice and I'd be happy with either.  

I have auditioned the Bartok on many occasions and feel it also is a nice DAC and worth the price of admission.  I don't feel it's better than the QX5/20 though.  

I own the QX5/20 and have used it for a while as a Roon endpoint on my network with an i5 core in another room.  Very nice sound much like @rossb describes.  Recently added a Wolf Alpha 3SX server to my rack and connected it by USB through the Wolf’s reclocking USB output.  I did not know the Ayre QX5/20 could perform at this level...  very rich tone now as well as the previously noted air and detail.  Much more muscular in presentation. 

I"ve heard it in uber systems and it's a great DAC/digital front end.  I will scale with better equipment to a very high level.