The REF 3 has a recommended minimum load impedance of 20K. The input impedance of the F110's balanced inputs is 202K, which is very high and won't be a problem, even in combination with the additional load presented by the input impedance of the main power amp (assuming the input impedance of the power amp has at least a little bit of margin relative to the 20K minimum).
The input impedance of the F110's unbalanced inputs, btw, is only 10K, which would be too low.
I assume, also, that you would be using the other of the REF 3's two balanced outputs to connect to the main power amp. That is preferable to using an unbalanced output to connect to one destination and a balanced output to connect to the other destination. The reason being that I'm pretty certain that the REF 3's balanced and unbalanced outputs are not independent of each other, the signal provided to the RCA connector being the same as the signal that is provided to pin 2 of the XLR connector, so using the RCA and XLR connectors simultaneously would introduce at least a slight imbalance of impedance levels and noise levels to the XLR's balanced signal pair. That won't be an issue assuming you are using the XLR outputs for both destinations.
A final point: If the length of the cables to either destination (main power amp or sub) is particularly long, make a point of choosing low capacitance cables (e.g., something like 25 pf/foot or less). The sum of the capacitances of the cables to BOTH destinations, if great enough, could cause at least a slight rolloff of the upper treble content of the signals received by the main power amp, by interacting with the 600 ohm balanced output impedance of the preamp. I wouldn't have any concern with pretty much any reasonably designed cable, though, if the TOTAL of the lengths of the runs to the BOTH destinations is say 25 feet or less.
Enjoy! Regards,
-- Al
The input impedance of the F110's unbalanced inputs, btw, is only 10K, which would be too low.
I assume, also, that you would be using the other of the REF 3's two balanced outputs to connect to the main power amp. That is preferable to using an unbalanced output to connect to one destination and a balanced output to connect to the other destination. The reason being that I'm pretty certain that the REF 3's balanced and unbalanced outputs are not independent of each other, the signal provided to the RCA connector being the same as the signal that is provided to pin 2 of the XLR connector, so using the RCA and XLR connectors simultaneously would introduce at least a slight imbalance of impedance levels and noise levels to the XLR's balanced signal pair. That won't be an issue assuming you are using the XLR outputs for both destinations.
A final point: If the length of the cables to either destination (main power amp or sub) is particularly long, make a point of choosing low capacitance cables (e.g., something like 25 pf/foot or less). The sum of the capacitances of the cables to BOTH destinations, if great enough, could cause at least a slight rolloff of the upper treble content of the signals received by the main power amp, by interacting with the 600 ohm balanced output impedance of the preamp. I wouldn't have any concern with pretty much any reasonably designed cable, though, if the TOTAL of the lengths of the runs to the BOTH destinations is say 25 feet or less.
Enjoy! Regards,
-- Al