i’m currently using a sblive, but i’m not too happy with it’s sampling quality from analog in.
one can get an used audigy1 at ebay for ~10 bucks these days, thats exactly my budget 
but does the audigy have much better ADC than sblive, or wouldn’t it be worth the upgrade?
or is there maybe a better cheap used card to look for in that price range?
a santa cruz goes cheap too at ebay, i heared people say it’s a good card… but it doesn’t have asio as far as i know?
hmm… dunno, maybe i’m not that exacting, but my sblive “value” is pretty good too me, i got -80 db noise with old russian microphone, that’s more than enough to me. there are also some details in different chip revisions like 16-18 bits ADC/DAC resolutions and etc. old revisions got 15.5 bits playback instead 16. imho the only actually minus of sblive is low size of microcode memory. but anyway, i’m not exacting in hardware quality…
hm well, i get much worse noisefloor even with line-in, mic-in is of course even worse. but noise isn’t so much my problem, it’s more how the sampled sounds… not clear, mudish, a bit distored. i doubt that the adc really distinguishes between the 65k possible different levels.
on the other hand i mostly sample from vinyl, so maybe it’s my shitty amp which causes distortion.
sounds weird… i think you should check your wires and all the hardware. distortion could be audible when DC offset is very big, you should be sure if your hardware got right line output voltage and it ain’t broken in general. also you can check your DAC bit resolution in some editor like Wavlab or just use zooming.
also check your card’s drivers and mixers, the best way is use kx dsp editor to check if there is any filters in the bus.
dc offset is small… my amp output level seems to be ok, however i do have not good and pretty long cables, so i’m not surprised about noisy recordings but i don’t know if this is the reason for the distortion.
i always thought it makes sense to get a new card every 5 years anyway, as quality improves a lot over time… i remember the card i had before the sblive, it was a terratec mejestro 16/96 and i was completely happy with it’s sound, didn’t notice anything bad about it… only reason for me to get a new card was directx compatibility. but when i had the sblive builed in, i was blown away b/c i suddenly noticed how bad the old terratec card really sounded 
have you used an old russian microphone with it?