Bad timing for me on this one or I could actually be a fair amount of help.
I've just replaced the stock Bart MM pickup in my Modulus Sonic Hammer with a complete Basslines pick up and harness. I've also got a heinz-ray made from pre EB parts on a lightweight 2 piece '93 body, including the original pre EB pickup and 2 band eq.
If you want to email me directly in a few weeks, I might be able to shed more light on comparisons with the stock pickup. But with the Bart and the Seymore there was a significant difference.
The Bart MM and Bart 2 band eq was very cutting and extremely aggressive sounding compared to the basslines, lacked a lot of warmth in my opinion. However my Akai SB-1 tracked it perfectly with no fudged notes whenever I played it.
Then I bought a basslines preamp which didn't really match up in terms of character with the bart pickup. So now the Sonic Hammer has got a basslines mm pickup instead. The sound is pretty much as has been already described above - growly, punchy, clean but not brittle and it oozed 'stingray character'. Of special note is the sweetness of the treble - there enough for clarity but its not brittle. In fact I could swear there was even a slight compression effect - all the more important bearing in mind that the neck on the modulus is graphite.
The pre EB pickup from the limited amount of time I played it (prior to dismantling what remained of the bass), was very full and powerful but with less midrange growl than the basslines. I know Ive tried other pre EB rays which had more bite but I wasn't looking for that kind of tone. It felt like I would start rearranging furniture with a few blasts from the open A string. Quite lovely and exactly the 'Nard Edwards tone I had been hoping for. When eventually teamed up with the all-valve Burmans, it should be a powerful combination.
But like I said, I can give you a better description when I've finished rebuilding the bass in a couple of weeks (once the 6 bolt neck plate arrives).
Cheers