I discovered this issue way back with Sennheiser Momentums. Even created a bug with Apple (and Sennheiser) about it. Sennheiser told me they can't reproduce it, Apple did nothing. The same happened later with B&W P7 and B&W PX. I believe the implementation of aptX in Apple's bluetooth stack is simply faulty, artifacts are very audible with test tones. However IRL I have not had a problem with quality, be it aptX or AAC (even SBC sounds good when the bitpool is high enough). One problem I do have with my new Amiron Wireless is bluetooth range - with aptX it is vastly inferior (unusable) - I literally take two steps from my Macbook and it starts dropping out. AAC is better, but still not that good. My P7 reached with aptX the same as Amiron does with AAC, and the P7 has much greater range in AAC (50% more would be my guesstimate).