If you're going for more Vintage type and 80s tones, you might try the JJ803s- it has a clearer type gain in some preamps,but I've never heard it in a JMP1 but it seemed to minimize the Diode Clipping or mask it in my Hughes and Kettner Tubeman- meaning it now sounds much more "tubelike" and rich with the JJ803s.
Since the JMP 1 uses diode clipping as well- the JJ803s might be the perfect tubes for it- they have a huge plate- different construction etc. and may overshadow the diode clipping as well and provide even more convincing tones.
Haven't tried the JJ803s in my ADA MP1 'cause it sounds very good with the JJ83s .
I don't play metal though- so I do Plexi and Marshall and Modded Marshall smoother stuff.