Hi Mike
It may be easier to list the ones that don't work. The sound card minimum requirements for Softrocks are truly that: minimal.
1) Stereo in and out
2) 16 bit or better
3) 48 KHz sampling or higher
If you spend $20 you have probably spent too much.
With 24 bits you get more dynamic range and with 192 KHz sampling you will see more of the spectrum. But your $15 16 bit card is going to hear everything the more expensive ones will.
If you have been a member for a while you have probably seen me recommend this before: Buy a cheap USB card and spend your money on antennas!
Good luck.... and don't over-think the card.
Warren Allgyer
9V1TD
Warren Allgyer