Intricate,
To make the comparison fair, you should place your two speakers side by side. It could be that one of the speakers is in a location where boundary reinforcement emphasizes the bass output more.
Moreover, a tube preamp's frequency response is rarely linear or smooth, especially compared to solid-state, so unless you measured the frequency response of the tube preamp, it could well be the contribution of the tube preamp that's emphasizing bass. Typically, the generous amounts of harmonic distortion from tube gear sometimes adds a "warmth" to bass reproduction.
By the way, you can ignore that Ninja site. The info there is simply wrong. And as kcarlile pointed out, cable length will have no influence at all.
Regards,
Alan
