After you mentioned the sibiance, I thought there may be some integration issue between the drivers and it is much easier to get this right with the right measurements. Pehaps you could change the polarity of one of the drivers and see whether it sounds "right versus wrong" or just different and still not right.
If you use one half (just the woofer's part) of a well designed crossover (assuming your box resembles Zaph's), then leave the woofer there and tweak the tweeter till it sounds right. I would start by choosing an L and C that give a rolloff at the same frequency and slope as the woofer is supposed to be at, then tweak the L-pad down, being careful to keep it at the right total impedance, till the tweeter just disappears from being the focus of attention, then tweak the L and C a little more.