Seeing how he rated Bose so highly, and it is his first IEM, I can see why he thinks the S4 lacks bass.
First of all, I am a Bose hater because of the horrible sound quality and price of their products. I've actually heard most of Bose's products, including the triports. The only way to describe the triport's sound is an ocean abundant amount of bass. It is more bass than you can ever imagine. It is a true subwoofer to your head level of bass. The OP is correct that the S4 has "underpowered" bass, because his reference point is the triports.
What I don't agree is saying the Bose sounds good. There is far too much bass in the music to the point treble is completely drowned out. I wouldn't be surprised if there is zero response above 7KHz.