how do you know if you need a dac ?

have always been into vinyl and recently decided to get out of it and bought a Ayre CX-7 cd player.    while it sounds just fine, I read in the forums about members getting dacs.         

how do you know if you need one or not ?

what benefit would one add if any ?
"Preamp is rca only, so if I wanted to try the xlr from the Ayre , would have to get the adapters.....and not sure if would make a difference ? could try I guess."

Don’t do it. adapters may degrade the sound ,rca are good enough. Your player has already very good build in dac IMO you don't need standalone dac.
I was using CD transport/player as a means to feed into pre-amp/integrated amp to listen to music for many-many years.

For me, below things pushed me to use DAC and get rid of my CD transport:
a. My CD-transport couldn't handle hi-res audio ( I use HDTracks to buy my hi-res audio) .
b. I was getting tired of getting up everytime I wanted to change the CD and listen to a different album/track.

Now, I have connected my laptop (running JRIVER - with all my CD ripped + Hi-res audio) into the DAC and can select/change tracks on my phone, while sitting on the sofa, sipping beer. I am exploring/enjoying old music, which got lost in the heap of CDs previously.

All the best with your decision.
How do you know that you need a DAC?  that's easy.
I have come the same route, that is, from vinyl.

You know you need a DAC when you find that, no matter what you have invested in your digital set-up, you find yourself returning almost all of the time to your vinyl.  When you find the right DAC, and that does not mean that you have to spend a fortune, you will want to listen to your digital collection at least as much as to your vinyl collection--because of the convenience.  I found such a DAC; othrs have found such a DAC. For me it was a long and convoluted road through digital before I wanted to listen to digital as much as to vinyl.  

I strongly second the suggestion of @ssnkssnk.  Eventually you will want to rip your digital to files and play through some sort of streamer set-up.  Not only will it be ridiculously convenient, but the SQ will exceed that of silver disk playing.

As far as I know, Ayre uses a delta-sigma or single-bit processor. One reason you might want to try a DAC is there are multi-bit non-oversampling (NOS) DACs out now that generally seem to please analog folks more than the upsampling single-bit DACs. You can try a Metrum DAC from HiFi Heaven or a SW1X DAC that uses tubes in the output stage. They both offer an in-home trial, so read the reviews and see which one sounds more like it meets your sonic priorities and give it a go. As a vinyl guy, I’m almost sure you’ll prefer one of these DACs to your Ayre. Obviously you can use the Ayre as a good transport.  Oh, and you probably want to invest in an Emprical Audio Synchro Mesh reclocker to get the best out of your DAC.