He has moderate aortic stenosis which means he needs medical therapy but no surgery yet. Also the ascending aorta is within normal limits, so this does not need surgical intervention. How severe is the aortic regurgitation: if it is severe than he may need valve replacement, but it does not sound like it from the LV dimensions
His EF of 48%is low however, without any good explanation. His stress test was likely non diagnostic because of insufficient heart rates. But he may still benefit from a left heart catheterization because of his diminished ejection fraction and diabetes and age.
Does he have atrial fibrillation? With the enlarged left atrial size he is at risk for this, and if not rate controlled this condition can cause a cardiomyopathy.
I'm looking forward to reading your answer. On the subject of screening BAV relatives... Because of my 15 yr old son's BAV, mod/severe AI and dilated asc AO, we had immediate family screened and younger son and husband came up with dilated asc aortas It can run in families. There is a convincing study that you can find at The Bicuspid Aortic Foundation's website. Good luck to your husband.