Is an Async DAC Needed to Reduce Jitter when playing CDs?

As an aside, technically, the best way to reduce jitter is to put a great clock in a CD player and co-locate the DAC in the CD Player chassis. Much of the problems with jitter and it's reduction occurs from having them live separately. 

But also, in the last few years the precision of inexpensive clocks has improved by several orders of magnitude, so there are many relatively inexpensive solutions now which are as pleasant sounding as the best of a decade ago. 

It's still important, but wow, so many good choices. 

Of course you need it. The digital interface is always jittery whatever the source.

Agree with shadorne, no source is sending a jitter-free signal to the Dac. And aren't all decent DAC's manufactured these days asynchronous?

You need a transport with an excellent clock to reduce jitter, or a memory player with a buffer for the data. IMO, the lowest jitter can be achieved by using a reclocker at the input to the Dac.
Of course, the Dac itself has to have a high quality clock.

Agree with shadorne, no source is sending a jitter-free signal to the Dac. And aren't all decent DAC's manufactured these days asynchronous?

It depends on what you call "decent", but by my standards, the answer is no.  I'm considering a used NAD M-51 and a Benchmark DAC1, neither of which is async.  The main reason I am asking is that my CD drive, a Cambridge CXU, does not have a USB Type B port.  As far as I know, asynchronous USB doesn't work with a standard USB 2.0 output, so I would not be able to get an async connection to my CD player.  I had heard that this is more of an issue with streaming output from a computer, but it sounds like that may not be the case.  The M-51 has an "Ultra Lock" technology that they claim eliminates virtually all jitter; that may be good enough, but I just don't know.