No, you shouldn't get that level attenuation. The manual states :
1/4-inch Analog Audio Outputs
These analog outputs accept balanced 1/4-inch connectors. The sleeve
is ground, the ring is negative phase (cold), and the tip is positive
phase (hot). Using an unbalanced 1/4-inch connector will reduce the
output by 6dB.
But if you use the XLRs to unbalanced 1/4" all should be fine.