Hi @Tom_Pawlik ----- Thank you for the report and my apologies for the troubles here. Dropouts can be caused by a variety of reasons as we have documented here in our knowledge base. More times than not, dropouts are related to some kind of networking or hardware performance issue. We recently had a case where a failing drive in a NAS had caused all sorts of issues for one of our users.
I see that you have provided some details of your current setup 
:
Roon v1.2
MacBook Pro; OSX 10.10.5; 4gb memory/2.53Hz
Tried same files on two external LaCie hard drives
Have about 6,500 “tracks” on the drives; all AIFF files;
DAC is the new Ayre QX-5
Thank you for this information. Can you confirm for me if all your media is being pulled from the drives mentioned in this description and furthermore, are you noticing the same behavior when playing content from local storage?
Moving forward, can you please give me a brief but accurate description of your network configurations/topology, as well as some insight into any networking hardware you may be implementing in your setup (routers, repeaters, switches, extenders, etc). The make and model of any of these devices would be good to have as well. I want to understand exactly how everything is communicating and receiving information in your setup. The more descriptive you can be the better 
-Eric