Regarding what one person here thinks we should expect, please let me clarify.
In addition to our 2014 Avalon, we also have a 2006 Camry LE, and my 90 year old mother in law drives a 1998 Olds 88 with a $78 after market radio/CD, but the original 88's speakers. Both of these "low end" systems compare to the Avalon like a Bose home theater does to a Sony Walkman. Maybe it cost Toyota 78 cents for this system.
Maybe these systems were made by Takata Air Bag company. When a call comes in on my connected iPhone, the ring is so loud, you practically get blown into the back seat. (Do you think it could blow up like one of their airbags?)
We still totally enjoy the Camry. It has been a great car, but the quality of sound, along with other ridiculous shortcomings, errors, oversights, items missing, etc., makes us think Toyota no longer gives a damn about anybody other than a Camry customer. My daughter's 2012 Lexus has most of the same shortcomings as the Avalon, and both the Avalon and the Lexus have a great deal more road noise on the highway than the Camry. We regret the purchase of the Avalon to the extent that we will never buy another Toyota product. Their high point of manufacturing quality cars has passed. They are becoming another General Motors of a decade ago.
Would others with this damned audio problem please post it so we can get an idea just how extensive it is. I suspect that all Avalons without the JBL upgrade have audio quality just below a 7" tablet.