Best wiring config for sub + biamping?

I'd appreciate some advice on the best way to configure a powered subwoofer with biamped speakers in a two-channel system. My system comprises a pair of Spica TC-60s with biampable inputs, a Mission 700as subwoofer, an Adcom GFP-555 preamp, and a pair of Adcom GFP-5200 power amps. The preamp has a processor loop and two pairs of line outs.

I want to use the sub's crossover to take the low bass load off the Spicas to clean up the midrange. And, I'm thinking of using one power amp for treble and one for midrange, rather than one amp per speaker. What I don't know is whether the sub's crossover will introduce phase shifts or other degradation, and if so, how to minimize this.

As I see it, there are three basic approaches.

1) Route power from one power amp to the Spicas via the sub's high-level inputs and outputs and run the other power amp straight to the Spicas, with separate line outs from the preamp to each power amp.

I'm thinking it might help to route the treble amp through the sub, as I'd prefer to keep the midrange signal as pure as possible to keep the Spicas' spectacular imaging intact.

2) Insert the sub's filter into the preamp's processor loop via low-level interconnects to and from the sub's line in & out jacks.

I'm wondering if there's a sound quality advantage to using the sub's low-level connections rather the high-level connections. This approach is simple, but will pass on any crossover distortion to both power amps.

3) Route one pair of line outs from the preamp to the treble amp and on to the speakers, and run the second pair of line outs to the sub's line in, then plug the midrange amp into the sub's line outs.

This avoids a high-level connection to the sub and keeps the sub's crossover away from the treble while still unburdening the Spicas of the lowest bass. On the possible downside, the crossover may now color the midrange.

Based solely on theory, I'm inclined to believe that setup 1 will yield the purest sound. However, as I don't really know whether the sub's crossover is actually going to introduce issues, and I don't know whether there's any advantage to low-level vs. high-level connections, I'm a bit at a loss here. Any comments about theoretical or practical factors would be much appreciated.