This wireless player reference design based on the K22 has the following characteristics:
Stable Bluetooth® connection and data transfer. Ultra-small size with a 3.3 x 3.3mm to 5 x 5mm small package provides more flexibility for product shape design. Ultra low-power Flexible extensions. MCU pin-to-pin compatible enable internal storage space upgrade without the need to modify hardware.
K2x USB MCU Family - Fact Sheet