Due to the inherent inadequacy of the D/A converters of an all-digital hearing aids to process, without audible artifacts, the normal transient peaks of live music. Even unamplified acoustic guitar and the human voice cause this defect in my all-digital aids to manifest itself. Tragically, I broke one of my 332s last year, and have since found nobody capable or willing to repair them. I wish to stockpile them so I can have a lifetime supply, and parts to salvage for repairs.
I have spent 2 and a half years, over 6 thousand dollars, innumerable visits to my audi, and am on my second model of all-digital HA, without satisfactory resolution of this issue. I have one 332 left, and I want to find more. As a musician and live music lover, this is of very high importance to my health and mental well-being. 
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I think he explained the reason very well. The same reason I bought an analog aid, for music.