First of all, you'll need TWO 1/4 shielded cables (the shorter the better) to run from the F-1X to the SVP1500 power amp.
Here's what you do: Cable #1 will go from the Crossover LOW pass output on the back of your F-1X to the INPUT of one of the channels of your SVP1500 (it doesn't matter which one). Use THAT power amp channel to drive your 18 cab ONLY. Similarly, cable #2 will go from the Crossover HIGH pass output on the back of your F-1X to the input of the REMAINING channel of your SVP1500. Use THAT power amp channel to drive your Triad cab ONLY.
One important detail: BE SURE that the stereo/Mono Bridge switch on your power amp is set to the stereo setting. Also, regarding the 2 level controls on the FRONT of your SVP1500, you might want to start out with BOTH of them set fully clockwise. Having done so, the Volume control on the front of the F-1X will function as the overall LOUDNESS control for the entire rig. If you find that by setting both of the level controls on the SVP1500 fully clockwise causes the Volume control on the F-1X to be just a bit too hair trigger for you, then back down on both of the SVP1500 level controls EQUALLY.
As for setting the frequency point at which the crossover will split the lows from the highs and send them to their respective power amp channels/speakers, the Frequency knob on the front panel of the F-1X (second knob from the right) handles that task. There's no hard rule as to what the crossover frequency should be, but you might want to start out by setting it at around 200Hz or so. See if you like the overall sound, but if you want to play around with it a bit, adjust that same control in SMALL increments. Also, the HF level knob on the front panel of the F-1X (far right) will function as a level control for the Triad cab ONLY, using this setup. Setting it counterclockwise from the 12:00 position will cut the output, and clockwise from 12:00 will boost the output. You might want to start out with it set at 12:00, and go from there.
Have fun!
