As you say, A2DP is Bluetooth’s standard for stereo audio, and it allows for optional codecs. SBC is standard, and aptX is among the optional ones in use (note aptX has more than one variant).
It appears that Broadcom was an early licensee of aptX, but CSR (Broadcom’s main competitor) purchased the company behind the technology in 2010.
Broadcom and Widcomm do not advertise aptX support. If aptX is important to you, I’d recommend getting an adapter using a CSR chipset, since CSR now owns the technology and it’s not clear how widely it will be licensed.
It’s one of these things that appears it will always be fragile – since it’s not a required or tested part of the Bluetooth standard, each layer involved needs to support it, and everything will fall back if anything doesn’t work out – it can be difficult to be certain how much effort is justified.
Thanks again for asking ahead … sorry I don’t have better news, and hope that background helps!