For what I know Matlab is capable of processing .wav files, so you could acquire samples from MIC IN line and then process the wav file in Matlab to verify your algorithm, but I don't know how to do it in Real Time ... I suppose you have to customize the audio card driver to do it.
There's a comand in matlab called wavrecord to record from the mic input
X=wavrecord(N,FS,CH)
Where,
CH:Number of channels, means mono or stereo
FS:Sampling rate to get samples
N:Number of samples to record then it stops.
If N=10*FS, then matlab will record 10 seconds.
and X is a row vector of the recorded samples.
u can playback the vector X by the comand wavplay
wavplay(X, FS)