I finally looked up the two tuners mentioned in your first post. I apologize for not doing that sooner, but you only recently made it clear that your AverTV HD Duet was tuning in some channels but not others. Your ATI Wonder 600 can receive analog cable channels but your AverTV HD Duet cannot. On the other hand, your AverTV HD Duet can receive Clear QAM (unencrypted digital cable) channels but your ATI Wonder 600 cannot. I presume your cable provider does have some Clear QAM channels, since you said the HD Duet was getting maybe half of the channels you expected (unless those were all over-the-air ATSC via antenna). Having both tuners installed would require a cable split, but should be possible.
Before shopping for more hardware, consider that U.S. cable providers are moving in an all-digital direction. U.S. OTA broadcasts have been digital since 2009, but cable providers have maintained downconverted channels for the benefit of customers with analog TVs that haven't worn out yet. In my area, Mediacom went (nearly) all-digital in December. They now provide only 13 analog channels (local, WGN, shopping), all of which have QAM equivalents; and in most cases I have my choice between standard-def and HD versions, hence I don't use the analog channels at all. Clear QAM is where it's at!
[Edit] Of course they make tuner cards that support analog, QAM and ATSC; but if they're all like my trusty old Hauppauge WinTV HVR-1800, you'd still need a cable split because they have two coaxial jacks.
Before shopping for more hardware, consider that U.S. cable providers are moving in an all-digital direction. U.S. OTA broadcasts have been digital since 2009, but cable providers have maintained downconverted channels for the benefit of customers with analog TVs that haven't worn out yet. In my area, Mediacom went (nearly) all-digital in December. They now provide only 13 analog channels (local, WGN, shopping), all of which have QAM equivalents; and in most cases I have my choice between standard-def and HD versions, hence I don't use the analog channels at all. Clear QAM is where it's at!
[Edit] Of course they make tuner cards that support analog, QAM and ATSC; but if they're all like my trusty old Hauppauge WinTV HVR-1800, you'd still need a cable split because they have two coaxial jacks.