Not a good idea. I have found a schematic for the HS 80 and the XLR and TRS inputs are simply wired in parallel thus, plugging in two AI outs will effectively load each one with the other's (usually very low) output impedance almost certainly causing distortion.
One solution, feed each output through a resistor in each "leg". Needs 8 in total each of about 470 Ohms (value not critical but must all be the same).
Better a switch. Must be 2 pole change over per speaker and some "dissing" of shields might be needed to beat hum loops.
ONCE again (again!) A simple bit of electrical and mechanical work for those with the basic smarts. Get some!
Dave.