Excellent playing and a beautiful bass / complete instrument(?!), but after listening to some of that stuff it made me remember why I sold my 7 and 6 string basses. The thinner the higher strings are, the less output they have and the lower notes just seem to dominate the higher ones -adding to the impression that the higher notes are thin and 'twangy'. You can of course use heavy compression to even out the extremes of volume across such an enormous octave range, but then the low notes will be too squashed.
At least with my old Chapman stick, having separate pickups and adjustable pole pieces meant you could achieve a better balance between all the strings -so maybe adjustable pole pieces on the pickups would be an easy solution.
Peace,
Rob.