You could always simply be choosing unequal volume settings between the two preamps, maybe unconsciously, based on their sounds. But it could be that the SS preamp is just doing a better job of driving your interconnects and amp inputs, which would presumably be due to its lower output impedance, not higher or lower gain (which is ultimately limited by where you set the volume control anyway, usually well below the available maximum).
In other words, even if you were to volume-equalize the two preamps at 1,000 Hz (the ear's most sensitive range), the tube preamp might suffer from an impedance mismatch - relatively speaking - driving its load as compared to the SS preamp, which would tend to slightly roll-off its response in the 'power range' of frequencies below the midrange which give music its "balls", as you say, causing it to sound a bit more lightly-balanced.
Another possibility (not mutually exclusive) is that the tube pre is suffering from a bit of dynamic compression, again relative to the SS pre, which is limiting its amplitude response on musical peaks and making it sound 'quieter' overall (in the sense of being less loud, not less noisy). Time for new preamp tubes, maybe? But even if neither of these scenarios is the case, SS preamps will commonly have somewhat firmer low bass than tubed models, and also better S/N ratios, and I suppose the results could sound like "more balls" to some listeners, even if volumes were broadly equal.
