I feel I'm being trolled, but anyway:
Really? Do you have a lot of experience recording an instruments through your integrated soundcard? I'm glad buying this new soundcard wouldn't improve the audio quality at all, so now I don't have to spend the money.
You overestimate the improvement you will get, or underestimate the quality of your line in. Try recording through your normal line in first. Even the shittiest onboard has a perfectly fine SnR for normal up to semi-professional recording. I pass the audio from my gamecube into my PC's onboard line in then out to my headphones, it sounds perfect. The noise is imperceptible unless you max the volume (my headphones go deafeningly god damn loud at max volume) and have silence coming from the gamecube. Even then it's almost impossible to hear it. Your experience won't be any different.
Didn't you once say you can't tell the difference between a 192 kbps audio file and a FLAC file around 5x the bit rate?
Simply stating a bitrate is not enough; samplerate, channels, compression format, compression settings and the piece of music that has been compressed are required for that.
Assuming you mean MP3, in most cases LAME-encoded MP3 above 192kbit/s is
transparent. I'm not sure you understand how lossy audio works; it strives to remove parts of the sound that humans
can't hear. AAC or Vorbis at 192+kbit/s are
transparent.
Waste some money on the card if you feel like it, you will get a negligible improvement since your onboard line in is fine.