how do you know if you need a dac ?

The Ayre CX-7 has also 2 xlr and unbalanced analog outputs,You should try them and see if the sound is better than the digital xlr you should use it instead. usually in this level CD players have very good build in dac I am not sure you need standalone dac for your system.

"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.