Okay looks good. 
No you shouldn’t need to go through your soundcard. Recording from X1800 channels 9+10 is the most direct way from the mixer to your computer. You could test with your soundcard using the digital out RCA or analog recording RCA’s to see how those levels turn out. You could also try the USB2 (if there would be something with the connector or perhaps cable; however you do see the X1800 soundcard as selectable…).
The only setting that would be affecting your current setup is the USB output level. You have it at +6, so that’s even louder than mine; which should be giving you a higher level in Audacity.
Thing is, do you even hear the real vinyl track or is it all static and noise??
Please check this also (but you seem to not get the error): X1800 and Audacity connection setup. I need help - #40 by Reese
(off to bed, will check in the morning)