i suggest you try a jumpered, single-wire configuration with your new cables and see if that makes any difference in the bass. This means you put the jumpers in and connect both + leads to one of the speaker's + terminals and both - leads to one of the - terminals. This should help you diagnose whether it is the cable or the biwiring that is giving you less bass than you used to have.
Your experience with trying just the one set at a time and not getting any sound at all is curious.
Your experience with trying just the one set at a time and not getting any sound at all is curious.