FunkMetal, ixlramp, thanks for your insights -- and TapyTap, thanks for the link. I think I read that ages ago. I'll have to go back and re-read it.
I just played the bass for awhile, and experimented with EQ at the amp and technique, which both help some. Don't get me wrong. The bass sounds good. Rich, nice midrange, yummy, organic finger-funk tone. I had a good time playing it, and received good feedback on its tone both when I tried it out on a "bass day" with some friends and when I performed live with it. (I'm still pretty new to six string -- still dialing in my technique and this bass, so it hasn't gone "out" much yet.) The strings seem responsive to nuances in touch, which I like.
What I'm hearing is subtle -- not sure how to describe it. If I pluck the open B and move from bridge toward the fingerboard as I go, I don't get only the expected change in tone from bright/midrangey to bassy/woody (poor descriptors, I know) but something floating above -- like a wah/sweepable filter. Really quiet, really subtle, but definitely there. Touch can help a lot. EQ helps some -- except in the case of a weird, boomy room, I don't like using EQ to "fix" a sound, but just to emphasize certain parts of a sound I already feel is fundamentally good and solid.
I have to experiment with this some more. I don't think I got a bad string (@ cassius 987), unless I got two -- but I took the B off this bass and put it on the bolt-on, where it's performing without issue. The B I replaced it with sounds just the same.
I'll play around with this (and maybe some different gauges later). I definitely like the balanced feel (love it on my Fender), but don't think I'd want to go bottom-heavy... though it is a novel idea.
-Mark