Alan -
I took a quick look at the manual.
When you do the trick with the jumper, you're not actually bridging the amp, you're doing a parallel input into both channels. This means the same signal goes into both channels, which are operating independently in parallel and comes out in the two outputs. If you had two cabinets, then you would hook one cab to each channel and you could control the blend between them by using the input level controls on the front of the amp.
You can use a stereo 1/4 to stereo 1/4 cable to jump or XLR to XLR, but they're both unusual cables because they're the same gender on each end.
If you want to minimize the number of weird cables to buy/build, then I would create an XLR-XLR jumper and you can use a regular (mono) 1/4 cable from the mono full range out of the F1-X to either 1/4 input on the power amp. The F1-X doesn't have a TRS output, and the 1/4 jacks are designed to take a balanced signal, so it woudn't be compatible anyway.
The more feature-rich QSC has true bridging selectable by switch which is a little different than the parallel input setup that the jumper gives you. In bridge mode, the + side of your signal is fed to one amp and the - side to the other, so the two amps are actually being combined into one. This increases the power of the one channel beyond the sum of the power of the two channels (this is as if the speaker impedance had been reduced). The amp is then only one channel, and you only connect to one speaker jack. You can't easily do this without modifying the circuitry inside the amp.
For what it's worth, I've always liked the results of running my rig in full-range mode, whether bridged or paralleled. For a bass amp, even the high treble is every other instrument's low end, so you don't get the kind of win by splitting the sound as you do in a PA system where you are driving wildly different speakers for highs and lows.
Hope this helps,
David Fung
