When a bassist I was roadieing for asked my input on upgrading his '76 P-bass, the first thing on my list was to replace the DirtMarzio he had in it with P-J Barts.
As I said above, I think a bass should have modern, hi-fi sound - which means clean, which ain't what DM does (I mean, they made their name with the "Super Distortion" & "Distortion Plus"). You can always add dirt later in the chain, but if it's at the source you can't take it out.
Just to ramble a bit, the Barts had active electronics; V-P-B-M-T. The fretless maple 'board was replaced with ebony (shortly later Jaco-poxied) with LED markers. The Bad-Ass he already had on it. That was, IIRC, '81; it's still his main ax.
Also, one of his 8X10" SVT cabs was converted into a 1X15' enclosure in the middle, with 2 2X10" enclosures top & bottom*; the other was swapped out for an 18" folded horn. The SVT head was sold to fund a Furman pre-amp & Ashley 3-way crossover (or maybe that was the other way around; like I said, it was '81.....) and a Yamaha (of course) power amp for the 10s & 15. The 18 was pushed by the amp section of an Acoustic head; I disremember the model.
Put all that together with his ears & fingers and it was absolutely awe-inspiring! (I will note that, while the P is still his #1 - #2 being an Ibanez fretted I sold him a couple years later when I worked at GC - as he is pushing 70 & no longer has me to hump it, he no longer uses that rig.......)
*Last I heard, the guy I took him to for that liked the challenge - but swears he'll never do the like again, and is still kinda pissed at me for bringing to him.
Peter