I have had my Etymotic XR4s since 2018, got them to replace ER4s I had had for at least 10 years before that. Back then the XR4s were lower impedance, not necessarily “Bass Boost.” An adapter cable was available to increase the input impedance to bring the XR4s up to the flat response of the ER4s. Correct fit has always been critically important to getting good sound out of these earphones. I was very dissatisfied with the poor bass, tinny highs, and lack of clarity when I got the XR4s (the ER4s always being excellent). I finally settled on the Comply ear tips for XR4s as giving the outstanding audio performance I expected, at the expense of some isolation (not enough to bother me). I do the trick of pulling my crusus up and back when inserting the ear tip. I push it in firmly. It takes some getting used to, having something that deep in my ear canal (and getting over the fear of “will I be able to get this thing out or will it be left in there*). If it hurts, something is wrong. You may have to build up tolerance. Start with a rock single. Work up to a symphony. Recently I discovered that my left ear takes a size smaller ear tip than my right. Sounds even better now. Trial and error, patience and perseverance. Eventually it becomes habit. *- in the EXTREMELY RARE event an ear tip (of any kind) remains behind in your ear canal, a steady-handed son with a pair of needlenose pliers (the dullish kind, not the super thin sharp kind) will make short work of it.