As Diabloblizzard stated, it's not generally a difficult job for an avionic engineer to either view and listen to or download all of the CVR and FDR data.
On our maintenance schedule, there is a 12 month CVFDR inspection which involves checking that the FDR parameters have all been recording satisfactorily and that all of the CVR channels have good clear audio quality.
One point worth mentioning is that some companies have fairly strict policies in place limiting who is allowed to access the data and what they can do with that data and with the company that I work for, there is a requirement to obtain the written permission of any flight crew who are recorded on the CVR prior to listening to it. (This is only for maintenance purposes. No such permission is required if the access is because of an accident or incident).