DL is offering you sound advice.
As you have already shown with your first antenna purchase, mileage claims can be made with little if any scientific evidence to support the claim. In fact, I submit that the science would disprove the more fantastic advertising claims.
When dealing with reputable antenna manufactures, mileage claims can be somewhat helpful (to a non-technical sales person and non-technical customer). When legitimate gain figures are available together with a reasonably accurate signal strength prediction (Thank you TV Fool), a far more accurate estimate of performance can be made. DL has access to both your TV Fool report and the gain figures for the antennas he has suggested. (You have been offered the fundamental parts of an engineering study that would have cost hundreds or thousands of dollars a few years ago if you had hired an engineering firm to do an analysis of your reception conditions.)
As far as going "through the cable box" is concerned, are you describing a structured cabling terminal like this...
http://www.twacomm.com/catalog/model...561DDF699489C4 that is the central distribution point for data, phone and TV in your home?
I feel the need to caution against connecting your antenna to any part of an active cable TV network. If you do, you risk causing harmful interference with aviation communication and navigation services, police, fire and other life safety services could also be affected.
DL has suggested, and I agree, try without an amplifier. An amplifier that is not needed actually reduces the quality of all the signals.