Hi Greg,
One thing you can do is try running the high output of the crossover through an effects unit and leaving the low end clean. So it would be:
low output->amp channel 2, and
high out->effects unit->amp channel 2.
This lets you add effects like phaser (awesome), chorus, overdrive or delay to your sound without muddying up the bottom too much. It's a place to start, and I'd definitely recomend fiddling with that for a while before going to anything more complex. There is a lot of variation to be had with the crossover frequency knob, the low/high balance knob, and the volume of each amp channel.
Next step might be adding a 2-channel graphic eq, one for each channel, but I don't think you'll get much benefit from that; that is, I don't think you'll be able to do much more than you would be able to do with the tone controls on the f1x, although it might be a little easier to find what you're looking for with a graph as opposed to the 3-knob layout.
A Superfilter run in stereo would seem be more logical a choice than an f2b. The eq section is the exact same on both the f1x and f2b, so you're really just getting more of the same thing. The Superfilter lets you select between lowpass/bandpass/highpass options, the amount of boost at the selected frequency, as well as the ability to adjust the blend between the dry and equalized settings.
So if you have some money to spend, you could set up something like this, starting with your F1X:
Low out-> Superfilter ch.1-> amp ch.1, and
High out-> effects-> Superfilter ch.2-> amp ch.2.
You would definitely have plenty to play with there.
What sort of amp/cabs are you using now? Knowing that would really help us give better, more specialized input.
Hope this helps,
Charles
