Tom, sure it's preferable to limit the bass frequencies that the mains have to handle when a good sub is in use. Forcing the mains to still play full-range in that situation isn't disastrous, but the sub should play those frequencies both more strongly and more cleanly and allow the mains to play more cleanly in the frequencies they handle well.
In your setup you can get a reasonably good blend using the 85Hz high-pass filter on the F1000's speaker level outputs and applying a setting around 80Hz(assuming that the setting is reasonably accurate)on the low-pass filter(not a crossover, although that term is frequently used on the sub frequency control)knob. The blend obtained with the crossover setting in modern HT receivers is more precise, but if you don't want to get into that(which is fine even in 2.1 setups)and wiring the speakers directly from the receiver, you'll continue to rely on the sub's high-pass filter.
Also note that although many current subs do have speaker level outputs, very few have a separate high-pass filter on them, and simply feed the full-range straight through to mains if they're connected.
