Auscultation is just listening to the heart - usually with a stethoscope. That is the first step in detecting the presence of aortic or sub-aortic stenosis. That is, if a murmur is detected, the dog should then undergo a doppler echocardiogram to determine severity.
Cardiomyopathy isn't the only heart condition that boxers are prone to
But the symptoms and diagnosis of AS/SAS are quite different to BCM.
There is more on the diseases boxers are prone to, and the tests that should be undertaken in the following links: