HQPlayer has a very different design philosophy from JRiver. It moves the oversampling and sigma-delta processing that most DACs use into software, so that the user has more control over the processing parameters. As such, resampling is a normal part of its workings. If you accept the premise of HQPlayer, then resampling and upsampling is just routine. As such, resampling to 64 KHz is just a normal process, although to a somewhat unusual rate.
JRiver takes a different approach and processes in the normal sample rates that DACs use and therefore 64KHz is a complete outlier. JRiver leaves the oversampling and sigma-delta processing to the DAC.
There are arguments for both approaches. But it seems like changing JRiver to accommodate a sample rate that does not fit its core structure makes little sense. If 64KHz indeed becomes a widely used sample rate, then JRiver will probably need to incorporate it. But, I doubt that 64KHz will ever become a standard. DAC manufacturers are just not likely to add another sample rate into their products, especially those who use separate clocks for 44 and 48 KHz multiples. In JRiver's case, 64KHz a sample rates seems like nothing more than a way to save disk space, at the cost of lossy resampling and a more complex data path.
If the OP is wed to the 64KHz format, then, IMO, JRiver is not the player for him.
