Not really familiar with the QB-9 however I can say without a doubt that the Wavelength Cosecant is superior to the C5xeMP which I used to own. My brother says it is no contest vs. the C7 which he also owns.
As you may or may not know, the QB9 uses the proprietary Wavelength asynchronous USB technology - but I've heard from several people that the Cosecant is far, far superior - although of course it does cost more.
If I were in the market for a digital source I wouldn't buy a CDP - I do believe that the technology is on its way out and service on transport, laser etc is likely to become difficult in the coming years.