From their previous posts to the A'gon forum I would guess the OP might be asking about the Blue Circle Thingee, but that is purely speculation. Oddly enough it employs the TI PCM2706 DAC - I've just recently read a comment on a different product using the same DAC chip in its line-output that mentions some distortion when using the Apple volume control at the highest setting. The other product is an iBasso D4 Mamba portable headphone amp.
here's the thread that mentions it. I have not looked through the 50+ pages of input there to find out what it's about, but if the OP is indeed talking about the Blue Circle product you may want to invest time into checking that thread. It could have something to do with that specific DAC chip. If I'm wrong about the product, then all bets are off.