[cnvogel]

There is no audio card with 32bit ADCs available for a couple hundred $, and even if there would be such a thing, you would need a signal source with a low enough impedance to not completely drown in thermal noise.

Any application requiring that much precision will not magically be solved by connecting a cheap soundcard. For one, ADCs in soundcards do noise shaping, so there will be an artificial increase of noise at higher frequencies (just record at 96k or 192k and have a look). Second, the absolute precision will not nearly be as good as on an ADC for quantitative measurement: typically there is no low drift reference, also when you DC couple the offset will drift, too.

The only thing they typically do very well is the "real-time" part, because that's what audio software is optimized for... :-)