using an active crossover, w/adjustable wolume for at least one of the amps, makes things a lot easier. my current system uses a pair of larger vmps subs, crossed-over at 60hz, to a pair of meret re monitors. these monitors have an eton carbon-fibre woofer & a focal inwerted-dome tweet. i use a pair of bridged adcom gfa-555's to drive the vmps', & a pair of electrocompaniet aw60ftt's in a wertical-biamped set-up to drive merets. i have *no* problems w/the different amps, because the 60hz crossover point is effected w/a marchand 24db/octave active x-over. besides offering separate bass & treble wolume controls, it also offers a wolume control *at* the x-over point. this makes it easy to match differing amps w/differing slew & gain rates. i highly recommend using an active x-over in general, and for transparency at a reasonable cost, i feel the marchand can't be beat. while i don't have direct experience w/the well-regarded bryston 10b, for example, more than one person told me the marchand is more transparent, at half the price. the marchand is also more flexible, imho...
hope this helps, doug s.