I2S Stereo ADC Soundcard Hacking

My idea is to exchange two input signals (CH_L1_IN and CH_L2_IN) at the sampling rate (192kHz) to produce one signal (CH_L_OUT), sampled at 192kHz (small electronic cicuit cf https://electronics.stackexchange.com/questions/754648/i2s-stereo-adc-soundc...). In this way, in the digital domain I will receive CH_L1_IN, CH_R1_IN, CH_L2_IN, CH_R2_IN... Of course, the sampling frequency will be decreased by 2 using this method (96kHz instead of 192kHz). But the number of channels is increased by 2 also (4 instead of 2). Where can I begin with alsa to increase the number of channels and adjust the sampling frequency ? Something like a virtual soundcard maybe ? I have skills in dev but don't know where I have to start with alsa fot this hack...