We propose a new concept audio system, It is an audio system with slots for inserting function units in one main body. It is a group for producing the first product for standardization. (Network audio player, DDC, DAC, PHONO equalizer, PRE Amplifier, POWER Amplifier, POWER SUPPLY, etc.) The internal main board has slots for inserting the unit, and the corresponding unit can be installed and replaced with another compatible unit. Function units are made in card format and can be upgraded or replaced with other branded products in the future.