My main rig is a Phil Jones M-500 head, along with Phil Jones 8-T and 16-B cabs, and while I agree that Phil Jones builds perhaps the most neutral-sounding amp on the market, none of the Markbass amps I've tried sounded anything like my Phil Jones.
They sounded good (as did the EBS and SWR rigs I've owned), but had - to my ears - a processed tone that my Phil Jones does not. YMMV.
I've always thought that the M-500 was a brilliant amp, and the PJ cabs are something too- Never got to play thru PJB gear much except at NAMM (which sucks as a testing ground) but I THINK I could "un-process" my LM800T thru say my Bergie HS410 to get as much a neutral tone as I need. Of course it would not sound like a PJB...because its a MarkBass, and vice-versa!

C'mon Jimmy, it was a back-handed compliment!!