Your soundcard calibration is not valid, possibly because there was some monitoring active. None of the input signal can get back to the outputs. It is OK to measure without a soundcard calibration file if you are absolutely sure there is no monitoring.You can remove the soundcard calibration from existing measurements using the Change Cal button on the measurement panel and remove the file for new measurements by clearing it on the Soundcard preferences.
Measuring with both speakers has some validity at the low end, where much bass content may be mono anyway, but you should also measure each speaker individually. At higher frequencies driving both speakers causes comb filtering due to even slight differences in the distance from the mic to each speaker.
RT60 times aren't really meaningful below a couple of hundred Hz unless you are in a very large space. There looks to be a big room resonance at about 36 Hz, you may be able to reduce that by changing the speaker or listening position, or some EQ could be applied to tame it. The response below 150 Hz is a bit ragged, so some experimentation wit position would probably be worthwhile. If you happen to be in a rectangualr space the room simulator may help with investigating possible positions before actually moving anything. Make sure the monitoring is disabled before making any other measurements though.