I'm having the same trouble ... I note that the .aax file extension is perhaps the problem ... I'm using Windows and in Explorer under the type column these files appear as AAX files. They will not import into MC 20 but they will play in iTunes. Older Audible files have an AA extension are listed as "AudibleAudio Title" and import and play fine in MC 20 ... I'm waiting for a call from Audible tech support to see what I can find out about this ... I'll let you know if I get any new info.
News Flash: AAX is the new high quality Audible format and JRiver does not now and it looks like will probably never support that ... if you still want to play your books in JRiver, you need to download them from Audible in Format 4 instead of the AAX format ... then they will work ... there are a number of other posts in the forum on this topic that I hadn't seen when I posted to you earlier ....
