I am not sure how you could increase base with speaker cables unless you filtered the mid and high range.
In general, if loudness, EQ, room placement or a bigger amp can't do enough for your bass then I would suggest that the only practical way to get more base is to get a speaker with greater bandwidth or a sub (usually this means a bigger box).
A good sub can significantly improve bookshelf speakers bandwidth and fill a low end hole especially at low levels, however, there is still lots of energy in the 80 to 300 Hz range that a small speaker will have to deliver, which leads to a risk of higher distortion at higher listening levels as the small woofer excursion becomes excessive and ultimately unable to keep up with the sub output.