I have started thinking that async USB is not worth the hype for home stereo. IF you have to use a system, use a desktop with juli@ card. It is useful only if you want to use a laptop, as there isn't an option of a digital out, except USB.
A well implemented Asynchronous USB will be superior to co-axial connection technically.
There are Adaptive USB DAC's too which perform as good as some of the best Asynchronous USB DAC's.
It might cost about as less as $40 more for a manufacturer to give asynchronous implementation on their DAC's. Some asynchronous implementation may require some micro controller programming which all manufacturers might not have that expertise and in some cases the software implementation has to be bought from a third party vendor which the manufacturers might not want to bother as it increases cost.
Asynchronous USB is a good to have feature and there are many DAC's in the market which offer it.