I've been using an F1-X to drive various QSC power amps with great success for the past 8 years; utilizing the F1-X's front panel balanced XLR output for that purpose. Additionally, I utilize an on/off switchable Neutrik female XLR plug going into the F1-X's front panel, providing me with a very handy standby/mute switch. And since it's a balanced line-level signal, cable length is a non-issue...particularly if I want to position the pre-amp some distance from the power amp & speakers. And for those instances when a balanced signal is additionally required for the house, I simply utilize the un-used INPUT jack of the channel of the QSC receiving the F1-X's output signal for that purpose (since the QSC's inputs are wired in parallel, the unused input can function as an output). Doing so DOES require a short balanced patch cable with a male XLR plug on the open end, in order to match up with a standard mic cable running to the House. Furthermore, if attenuation is needed for the House signal, I utilize a Shure A15AS switchable (-15/20/25db) attenuator in-line to the House....-20db seems to keep the sound guys happy.
Utilizing the F1-X's XLR output for this purpose provides an additional bonus: being able to switch between Pre & Post EQ output, effecting both the Stage Amp and House simultaneously. And some folks insist that the F1-X is lacking in features.....!