monitors:
i personally prefer passive speakers, with a separate amplifier.
but i'm just that way..
my guitar rig is the same, tube head, separate cabinets, no combos.
reason:
if the amp goes bad in one channel, you'r down on your entire rig.
if a separate system amplifier goes down, you can always rent beg or borrow another amp until you get the broken one fixed.
also, it's cheaper to ship an amp to get fixed, than it is to ship an entire speaker cabinet with the amp built into it.
also, suppose you really like your amp, but decide you're ready to upgrade to another set of monitors?
also, no matter how well they say things are shielded inside the cabinet, any scientist can tell you that proximity to electric and magnetic fields are going to have SOME kind of effect.
to me, it's just easier to keep them all separated.
the problem with that, most recently, is that there just aren't that many really good passive systems anymore, most manufacturers have moved to a powered setup, because they know they've got you by the short hairs.