You have a vertical passive bi-amp set-up at the mo. If you are looking to fine tune, try horizontal - one amp for lows and one amp for highs. You may find that the stereo imaging is reduced (crosstalk) but the separation should jump up.
Another advantage of horizontal is that you are driving each side of the same amp an equal amount. With vertical, the LF side of the amp will be consistently driving significantly harder than the HF side.
If you listen at moderate volumes you should seriously consider active crossovers, as the woofers create back emf when moving hard, which muddies up the crossovers. Amps have circuitry to combat this, so putting the crossovers between the pre and powers eliminates the negative effects.
You can actually experiment with this without having to do any major surgery on your speakers. The crossovers will probably be connected to the drivers with spade connectors, so you can very easily bypass them, and binding posts can be found with screw clamps, making the whole enterprise easily reversible.
I have just gone down this route, and I have to say that the gains have been suprising. My poorly performing 602.5's actually sound like you would expect something that costs twice the price. Although be careful...as far as 'tweaks' go this is bordering on hi-fi hobbyist. It'll get you thinking about all sorts of things like building your own speakers and interconnects...but it will also make you much more of a stakeholder in the sound that your system produces - which is priceless.